Sunburn

Sunburn is an acute, transient, inflammatory response of the skin to excessive exposure to ultraviolet radiation (UVR). Sunburn results from natural sunlight or artificial sources (e.g., tanning beds, phototherapy devices.) (Picture 1)

The skin is one of the largest organs in the body in surface area and weight. The skin consists of two layers: the epidermis and the dermis. Beneath the dermis lies the hypodermis or subcutaneous fatty tissue. (Picture 2) The skin has three main functions:

• Protection
  • The skin is an organ of protection
  • The primary function of the skin is to act as a barrier
  • The skin protects from:
    • Chemicals
    • Mechanical impacts and pressure
    • Micro-organisms
    • Radiation
    • Variations in temperature
• Regulation
  • The skin is an organ of regulation
  • The skin regulates several aspects of physiology, including:
    • Acting as a reservoir for the synthesis of Vitamin D
    • Body temperature via sweat and hair
    • Changes in peripheral circulation and fluid balance via sweat
• Sensation
  • The skin is an organ of sensation
  • The skin contains an extensive network of nerve cells that detect and relay changes in the environment
  • There are separate receptors for heat, cold, touch, and pain
  • Damage to these nerve cells is known as neuropathy, which results in a loss of sensation in the affected areas. Patients with neuropathy may not feel pain when they suffer injury, increasing the risk of severe wounds or worsening an existing wound (White, 2022)

Sunlight is essential for synthesizing vitamin D. Sunlight also has beneficial effects on mood. However, ultraviolet (UV) radiation (290 to 400 nm) is responsible for several acute and chronic detrimental effects on human skin, including sunburn, photoaging, and skin cancer (Baron, 2021). (Picture 3)

Ultraviolet B (UVB; 290 to 320 nm) and ultraviolet A (UVA; 320 to 400 nm) can cause sunburn. Wavelengths that are the most effective at inducing erythema are in the UVB range (Young & Tewari, 2021).

UVB (290 to 320 nm), representing only 5% of the UV radiation reaching the earth's surface, includes the biologically most active wavelengths. UVB is responsible for: (Baron, 2021)

• Hyperpigmentation
• Inflammation
• Photocarcinogenesis
• Sunburn

Approximately 95% of the UV radiation reaching the earth's surface is UVA (320 to 400 nm).

• UVA contributes to photoaging, has a major role in pigment darkening, and may be involved in skin carcinogenesis
• UVA2 (320 to 340 nm) produces similar effects on the skin as UVB but only constitutes approximately 25% of the UVA band
• UVA1 (340 to 400 nm) is less potent than UVA2 and has a decreased ability to induce erythema (Baron, 2021)

Photoprotection is crucial to prevent or reduce the potential harms associated with UV exposure and includes: (Baron, 2021)

• Sun avoidance during peak hours
• Sun-protective clothing
• Sunscreens

Sunburn is common. In the United States (US), the estimated sunburn prevalence (≥ 1 sunburn in the past 12 months) among all adults was approximately 34% in 2005, 37% in 2010, and 31% in 2015. Prevalence ranging from 20% to 70% has been reported in cross-sectional studies in Europe and Australia. In the US, sunburn has also been reported in 13% of African Americans and 30% of Hispanics (Young & Tewari, 2021).

Sunburn occurs more frequently among adolescents and young adults. In nationwide surveys in the US, approximately 70% of adolescents aged 11 to 18 years and 50% of adults aged 18 to 29 reported at least one sunburn in the previous year (Young & Tewari, 2021).

Factors that increase the risk for sunburn include:

• Altitude- the higher the altitude, the greater the risk of sunburn as UVR intensity reaching the skin is greater (Young & Tewari, 2021).
• When the sun is high, cloud cover offers some protection, but significant quantities of UVR still reach the earth's surface (Young & Tewari, 2021).
• Having light skin, blue eyes, and red or blond hair (Sunburn, 2020).
• Mixing outdoor recreation and drinking alcohol (Sunburn, 2020).
  • In a study of beachgoers in Texas, participants who reported drinking alcohol on the beach had a greater body surface area with sunburn and blisters than nondrinkers (Young & Tewari, 2021).
• Nearness to the equator where the UVB intensity is highest. The risk of sunburn is inversely related to latitude and, therefore, greatest near the equator (Young & Tewari, 2021).
• Reflection from snow (approximately 90%), sand (15% to 30%), and water (5% to 20%) (Young & Tewari, 2021).
• Regularly exposing unprotected skin to UV light from sunlight or artificial sources, such as tanning beds (Sunburn, 2020).
• Taking photosensitizing medications increases the likelihood of sunburn(Sunburn, 2020).
• The time of day is important as sunburn is more likely to occur at noon than earlier or later in the day (Young & Tewari, 2021).
• Wet skin (e.g., swimming or spraying the skin with water) is more susceptible to erythema than dry skin (Sunburn, 2020).
• Working outdoors (Sunburn, 2020).

The magnitude of the exposure dose affects the extent and time course of the histological changes observed after UVB exposure.

• Epidermal changes include:
  • Spongiosis (intercellular edema between keratinocytes in the epidermis)
  • Parakeratosis
  • "Sunburn cells" (apoptotic keratinocytes with condensed nuclear chromatin and eosinophilic cytoplasm)
    • Sunburn cells may be present in the epidermis within hours of exposure, increase in number over the following 24 hours, and form a band at the stratum corneum at 72 hours
• Dermal changes include:
  • Endothelial cell swelling
  • Perivenular edema
  • Presence of degranulated mast cells
  • A perivascular infiltrate of neutrophils appears shortly after the exposure and peaks at about 14 hours. A later mononuclear infiltrate persists for at least 48 hours (Young & Tewari, 2021)

Patient Education:

• A clinician should be consulted if the sunburn:
  • does not improve within a few days
  • develops blisters on the face, hands, or genitals
  • is causing severe swelling
  • is blistering and covers a large portion of the body
  • shows signs of infection, such as pain, pus, or red streaks leading away from an open blister (Sunburn, 2020)

The patient should seek medical care if experiencing:

• a fever greater than 103 degrees
• confusion
• dehydration
• fainting (Sunburn, 2020)

Clinical manifestations of sunburn range from mild erythema to highly painful erythema with edema, vesiculation, and blistering. (Picture 1 above and Table 2). Blistering indicates superficial partial-thickness or, rarely, deep partial-thickness burn (Young & Tewari, 2021).

Erythema is usually first noted 3 to 6 hours following sunlight exposure, peaks at 12 to 24 hours, and in most cases subsides at 72 hours. The skin areas that were covered or shaded are typically spared (Young & Tewari, 2021). (Picture 1)

Increased skin sensitivity to heat and mechanical pressure is characteristic and present even in mild cases. In severe cases, systemic symptoms may develop, including headache, fever, nausea, and vomiting (Young & Tewari, 2021).

Based on the following clinical findings, the diagnosis of sunburn is usually straightforward:

• Painful erythema with or without vesiculation
• Blistering in exposed areas
• History of exposure to sunlight (Young & Tewari, 2021)

Contact with topical photosensitizers

• Some Potential Causes of Phytophotodermatitis
  • Plant Family: Apiaceae (Umbelliferae)
    • Common Names: Angelica, Celery, Cow parsley, Wild chervil, Cow parsnip, Hogweed, Dill, Fennel, Giant hogweed, Parsley, Parsnip
  • Plant Family: Rutaceae
    • Common Names: Bergamot orange, Bitter orange, Burning bush, Gas plant, Grapefruit, Lemon, Lime, Rue
  • Plant Family: Moraceae
    • Common Name: Fig
  • Plant Family: Fabaceae (Leguminosae)
    • Common Names: Bavachee, scurf-pea (Psoralea corylifolia)
  • Plant Family: Cruciferae
    • Common Name: Mustard
  • Plant Family: Ranunculaceae
    • Common Name: Buttercup
  • Plant Family: Hypericaceae
    • Common Names: St. John's wort (can cause systemic phytophotodermatitis)

Use of indoor tanning equipment

Exposure to UVB phototherapy or UVA photochemotherapy (PUVA) (Young & Tewari, 2021)

Several idiopathic photodermatoses may mimic sunburn. However, they can be easily differentiated from sunburn based upon their clinical presentation and time course:

• Polymorphous light eruption (PLE)
  • PLE is an idiopathic photodermatosis characterized by erythematous, itchy papules and vesicles occurring hours to days after sun exposure and persisting for several days (Young & Tewari, 2021). (Picture 6)

• Solar urticaria
  • Solar urticaria is a form of physical urticaria that presents with wheals or, less commonly, erythema alone after only minutes of exposure to sunlight and resolves within several hours.
  • Phototesting can confirm the diagnosis (Dice & Gonzales-Reyes, 2022).
• Chronic actinic dermatitis
  • Chronic actinic dermatitis is a rare, persistent photo-induced eczema that typically affects men over 60 years.
  • Many patients have a history of atopic dermatitis or coexisting allergic contact dermatitis (Elmets, 2022).
• Systemic lupus erythematosus (SLE)
  • The classic butterfly rash of systemic lupus erythematosus (Picture 7), which usually appears after exposure to sunlight, is frequently mistaken for sunburn (Elmets, 2022).

Intense, repeated sun exposure that results in sunburn increases the risk of other skin damage and certain diseases. These include:

Premature aging of the skin (photoaging)

Photoaging, also called extrinsic aging, is premature skin aging resulting from prolonged and repeated exposure to solar radiation. In individuals with light phototypes (see Table 2 above), sun-induced changes include:

• Actinic Keratosis
• Fine and coarse wrinkles
• Loss of translucency and elasticity
• Mottled pigmentation
• Sallow color
• Solar elastosis
• Solar lentigines
• Telangiectasias
• Xerotic texture (Chein & Kang, 2021)

In particular, in skin types I or II populations, atrophic and dysplastic changes (e.g., actinic keratoses) with fine wrinkling are common signs of photoaging. In skin types III or IV populations, predominant features include increased skin thickness, deep wrinkles, and a leathery appearance. Hyperpigmented macules and mottled hyperpigmentation are also common features of photodamaged skin in phototypes I to IV.

Other signs of severe photodamage include:

• Actinic purpura - also called senile purpura, or Bateman purpura, is a relatively common finding in older individuals with a history of excessive sun exposure. (Picture 8) It presents as ecchymotic macules predominantly located on the photodamaged skin of the forearms and dorsa of the hands (Chien & Kang, 2021).

• Actinic elastosis and cutis rhomboidalis nuchae. Actinic elastosis presents as a diffuse thickening and yellowish discoloration of the skin resulting from disorganized and damaged collagen and elastic tissue. It is typically seen in older individuals with fair complexion and a history of chronic sun exposure. On the posterior aspect of the neck, the formation of deep furrows results in a typical, irregular, rhomboidal pattern (cutis rhomboidalis nuchae).
• Poikiloderma of Civatte - presents as mottled pigmentation and telangiectasias involving the lateral aspects of the neck and the upper anterior chest in fair-skinned individuals with a history of high cumulative sun exposure. The submental area is typically spared.
• Favre-Racouchot syndrome is characterized by the development of multiple comedones on the periorbital area on a background of severely photodamaged skin. It is most commonly seen in older males with a light complexion and a history of chronic sun exposure.
• Idiopathic guttate hypomelanosis presents as multiple small, white macules that are typically located on the extensor surfaces of the upper and lower extremities. (Picture 9)

In photoaging in individuals with phototypes V to VI, the effects of photodamage generally occur 10 to 20 years later. They are less severe than those observed in individuals with lighter skin due to lower susceptibility to sun damage. In individuals with heavily pigmented skin, melanosomes increase in number and size, contain more melanin, are more widely distributed in the epidermis, and are more slowly degraded than in lightly pigmented skin, leading to greater photoprotection. With darker skin, premature aging typically manifests in the midface with prominent nasolabial folds due to increased skin laxity but fewer wrinkles. Prominent features in these individuals include:

• Dermatosis papulosa nigra
• Dyschromias
• Mottled pigmentation
• Seborrheic keratosis
• Solar lentigines
• Rough skin

While UV exposure is a major determinant of skin aging in individuals with light skin tones, its role is limited in those with highly pigmented skin. The changes of photodamage are superimposed on the changes caused by chronologic aging (the so-called intrinsic or programmed aging). They are responsible for most of the age-associated features of skin appearance.

Photodamage can be partially prevented and reversed with proper sun protection and various prescription medications. However, concerns about photoaging are primarily cosmetic and are influenced by geographic differences, culture, and personal values (Chien & Kang, 2021).

Precancerous skin lesions

Precancerous skin lesions appear as rough, scaly patches in areas that have been damaged by the sun. They are usually found on light-skinned individuals in sun-exposed areas of the:

• Hands
• Head
• Face
• Neck

These patches can evolve into skin cancer (also called actinic keratosis) and solar keratoses.

Skin cancer

Excessive sun exposure, even without sunburn, increases the risk of skin cancer, such as melanoma. It can damage the DNA of skin cells. Sunburns in childhood and adolescence may increase the risk of developing melanoma later.Skin cancer develops mainly on areas of the body most exposed to sunlight, including the following:

• Scalp
• Face
• Lips
• Ears
• Neck
• Chest
• Arms
• Hands
• Legs
• Back

Some types of skin cancer appear as a small growth or a sore that bleeds easily, crusts over, heal, and then reopens. An existing mole may change with melanoma, or a new, suspicious-looking mole may develop. A type of melanoma called lentigo maligna develops in areas of long-term sun exposure. It starts as a tan flat spot that slowly darkens and enlarges.

Other types of skin cancer include:

• Squamous cell carcinoma (SCC)
• Basal cell carcinoma (BCC)

Eye damage

Eyes, which are extremely sensitive to the sun's UV light, can burn. Too much UV light damages the:

• Cornea - Sunburn of the cornea is also called snow blindness.
• Lens - Sunburn of the lens can lead to clouding of the lens (cataracts).
• Retina

Sunburned eyes may feel painful or gritty.

Skin signs/symptoms may include:

• Skin feeling warm or hot to the touch
• Pain and tenderness
• Swelling
• Small fluid-filled blisters, which may break
• Headache, fever, nausea and fatigue, if the sunburn is severe (Sunburn, 2020)

Any exposed part of the body, including the earlobes, scalp and lips, can burn. Even covered areas can burn if, for example, clothing has a loose weave that allows the UV light through.

Sunburn signs and symptoms usually appear within a few hours after sun exposure. However, it may take a day or more to know how severe the sunburn is.

Within a few days, the body may start to heal itself by peeling the damaged skin's top layer. After peeling, the skin may temporarily have a distinctive color and pattern. A bad sunburn may take several days to heal.

Prevention of sunburn involves:

Sun Avoidance

Individuals should be advised to seek shade or reduce exposure to sunlight, particularly in the summer months and between 10:00 AM and 4:00 PM when sunlight intensity is greatest. (Young & Tewari, 2021)

When possible, try to schedule outdoor activities for other times. If unable to do that, limit time in the sun and seek shade when possible (Sunburn, 2020).

Photoprotective Clothing

Wearing clothes is important for sun protection (Baron, 2021). Protective clothing such as long sleeves and broad-brimmed hats should be worn outdoors (Young & Tewari, 2021). The degree of protection provided by clothes is defined by the ultraviolet protection factor (UPF), which indicates how effective a fabric is at blocking out solar UV radiation (Baron, 2021). Factors that contribute to the UPF rating of a fabric are:

• Color (darker colors are generally better)
• Composition of the yarns (cotton, polyester, etc.)
• Condition (worn and faded garments may have reduced ratings)
• Finishing (some fabrics are treated with UV-absorbing chemicals)
• Moisture (many fabrics have lower ratings when wet)
• Stretch (more stretch lowers the rating)
• Tightness of the weave or knit (tighter improves the rating)

The UPF classification is certified by national and international organizations (e.g., American Sun Protection Association, Skin Cancer Foundation). The categories are UPF:

• 15 to 24 for good protection
• 25 to 39 for very good protection
• 40 to 50 for excellent protection

A garment's photoprotective capacity may also be enhanced by washing with detergents containing optical whitening agents (Baron, 2021). Shrinkage from repeated washing and drying may improve the UPF.

Avoid Sun Tanning and Tanning Beds (Sunburn, 2020)

Getting a base tan does not decrease the risk of sunburn. Intentional tanning by using UVA tanning beds does not protect against the risk of sunburn (Young & Tewari, 2021). Although suberythemal repetitive exposure to UVA increases skin pigmentation (immediate tanning due to oxidation and redistribution of existing melanin), they do not increase melanin production and provide little or no photoprotection against subsequent UV exposures.

Liberal Use of Broad Spectrum Sunscreens

Sunscreens are topical preparations containing filters that reflect or absorb radiation in the UV wavelength range. Broad-spectrum sunscreens are generally combinations of sunscreen products that absorb both UVA and UVB radiation (Baron, 2021).

Broad-spectrum sunscreens with a sun protection factor (SPF) 30 or higher should be regularly used when performing outdoor activities, e.g., recreational, work, sports etc., in sunny weather, especially in regions with high insolation levels (Young & Tewari, 2021). Apply water-resistant sunscreen and lip balm with an SPF of 30 or greater and broad-spectrum protection against UVA and UVB rays (Sunburn, 2020).

Sunscreens should be applied 15 to 30 minutes before sun exposure to allow the formation of a protective film on the skin and reapplied at least every two hours and after swimming or sweating (Young & Tewari, 2021). It is recommended to wait for at least a few minutes (ideally, 10 to 20) following sunscreen application before dressing (Baron, 2021). In the US, the US Food and Drug Administration (FDA) requires the SPF to remain the same before and after water immersion, with the terms "water-resistant" and "very water-resistant," meaning that the SPF is maintained after 40 or 80 minutes of activity in water or sweating, respectively (Young & Tewari, 2021)

Sunscreens demonstrate a reduction in sun damage, squamous cell carcinomas, melanomas, and photoaging if used appropriately (Young & Tewari, 2021). If an individual is also using insect repellent, the sunscreen should be applied first. The American Academy of Dermatology does not recommend insect repellent with sunscreen products (Sunburn, 2020).

The FDA requires all sunscreen to retain its original strength for at least three years (Sunburn, 2020). Check the sunscreen labels for directions on storing and expiration dates. Throw away sunscreen if it has expired or is more than three years old.

Regardless of skin phototype, all individuals are subject to the potential adverse effects of UV radiation and benefit from sunscreen use (Baron, 2021). Sunscreens are beneficial for individuals with light skin (phototypes I, II, and III) who are more susceptible to acute sunburn and chronic (photoaging, skin cancer) adverse effects of excessive sun exposure. Light-skinned individuals should regularly use broad-spectrum sunscreens with an SPF of 30 or higher when performing outdoor activities in sunny weather, especially in regions with a high insolation level. Because individuals typically do not apply sunscreen in the recommended amount (approximately 1 to 1.5 ounces or 6 to 9 teaspoons per total body application), they may benefit from a higher SPF.

Sunscreen products with SPF 15 are generally recommended for daily use. Sunscreen-containing cosmetics (e.g., facial moisturizers, foundations) may improve photoprotection compliance. Most cosmetic products are formulated to provide an SPF of 15 to 30 and may or may not be labeled as a broad spectrum. Cosmetics providing broad-spectrum protection should be preferred to those containing only UVB filters.

The "Teaspoon Rule" (Baron, 2021).

Clinicians should instruct patients to adopt simple application techniques that ensure adequate amounts of sunscreen to the exposed areas. One of these is the so-called "teaspoon rule." It involves the application of:

• Approximately 1 teaspoon (visually measured) of sunscreen to the face and neck area
• A total of 2 teaspoons to the front and back torso
• 1 teaspoon to each upper extremity
• 2 teaspoons to each lower extremity

Benefits of Sunscreen

Skin cancers - There is evidence from observational studies and randomized trials that sunscreens prevent the development of actinic keratoses and squamous cell carcinomas (Baron, 2021). Clinicians counsel patients with sun-sensitive skin must type about sun protection because susceptibility to sunburn is a marker of genetic susceptibility to skin cancer and is associated with an increased risk of melanoma at all ages (Young & Tewari, 2021)

Photoaging- Skin damage from UV exposure accumulates over time. In fair-skinned individuals, a substantial amount of photodamage manifests by age 40. Sunscreens may prevent skin changes such as pigmentation and wrinkling attributable to chronic photodamage or photoaging (Chien & Kang, 2021).

Photodermatoses - Broad-spectrum sunscreens with high SPF are generally used to prevent photodermatoses, which can be elicited by either UVA or UVB (Elmets, 2022).

Protect Eyes - Sun damage to the eyes can happen all year long, especially in sunnier climates. UV-blocking sunglasses should be worn along with broad-rimmed hats when outside. Choose either 99% or 100% UVA and UVB protection or UV 400 protection sunglasses. UV rays also pass through clouds, so it is important to use sun protection even when cloudy. Check the UV rating on the label when buying new glasses. Never look at the sun directly, as this can cause severe damage to the retina even when cloudy. Darker lenses are not necessarily better at blocking UV rays. Wear sunglasses that fit close to the face or have wrap-around frames. Help children and the elderly to protect their eyes with hats and sunglasses.

Protect Infants and Young Children - Infants younger than six months should be kept out of direct sunlight. The American Academy of Pediatrics recommends using other forms of sun protection, such as shade or clothing (e.g., lightweight pants, long-sleeved shirts, brimmed hats) for babies under six months (Sunburn, 2020).

The American Academy of Dermatology recommends avoiding sunscreen products on infants younger than six months (Sunburn, 2020). Keep infants cool, hydrated, and out of direct sunlight. If sun protective clothing and shade are not available, sunscreen should be applied to infants and toddlers (Sunburn, 2020). A minimal amount of sunscreen with at least 15 SPF can be applied to small areas, such as the infant's face and the back of the hands (Baron, 2021).

Since infants have an immature skin barrier, sunscreen products should be non-irritating to the skin and eyes and have a low sensitization potential (Baron, 2021). Products containing physical blockers (titanium oxide, zinc oxide) should be used to cause less skin irritation (Sunburn, 2020). These products are preferred for infants and children because they offer broad-spectrum protection and have minimal irritation, sensitization, and skin penetration potential (Baron, 2021).

Awareness of Sun-sensitizing Medications - Some common prescription and over-the-counter drugs, including antibiotics, retinoids, and ibuprofen, make skin more sensitive to sunlight. A pharmacist or MD should inform the patient about the side effects of their medications (Sunburn, 2020).

Sunburn is an acute, delayed, and transient inflammatory response of the skin to excessive exposure to UVR from natural sunlight or artificial sources. Both UVA and UVB can cause sunburn. However, the most effective wavelengths in inducing erythema are in the UVB range (290 to 320 nm).

Clinical manifestations of sunburn include painful erythema with or without edema, vesiculation, and blistering. Erythema is usually first noted 3 to 5 hours following sunlight exposure, peaks at 12 to 24 hours, and usually subsides at 72 hours.

The diagnosis of sunburn is usually straightforward, based on clinical findings and a history of exposure to sunlight or artificial sources of UV radiation.

Sunburn is a self-limiting condition. Cool compresses or soaks, calamine lotion, or aloe vera-based gels may be used to relieve skin discomfort. For the treatment of skin pain and inflammation, oral NSAIDs are advocated.

Patients with extensive blistering sunburn, severe pain, and systemic symptoms may require hospitalization for fluid replacement and parenteral analgesia.

Sunscreens are topical preparations containing inorganic (mineral) or organic substances that reflect, scatter, or absorb UV radiation in UVA and UVB wavelength ranges. Broad-spectrum sunscreens are generally combinations of sunscreen products that absorb both UVA and UVB radiations.

Regardless of skin phototype, everyone is subject to the potential adverse effects of UV radiation and may benefit from sunscreen. However, sunscreens are beneficial for individuals with light skin (phototypes I, II, and III) who are more susceptible to sunburn, photoaging, and skin cancer.

Broad-spectrum products with an SPF of 30 or higher are recommended for individuals performing outdoor work, sports, or recreational activities.

Sunscreens must be applied liberally, repeatedly, and to all sun-exposed skin to provide effective protection. Simple, practical rules, such as the "teaspoon rule," may determine the adequate amount of sunscreen to apply to certain body areas. Sunscreen should be applied 15 to 30 minutes before sun exposure to allow the formation of a protective film on the skin and reapplied every two hours.

Sunscreens generally have an excellent safety profile, and there is no evidence of systemic adverse effects related to percutaneous absorption. For those concerned about systemic absorption of organic sunscreens, sunscreens that contain inorganic constituents (zinc oxide, titanium dioxide) can be recommended. Organic sunscreens may rarely induce allergic and irritant contact dermatitis, phototoxic and photoallergic reactions, or contact urticaria.

Wearing clothes is important for sun protection. The degree of photoprotection provided by clothes is defined by the UPF, which indicates how effective a fabric is at blocking out solar ultraviolet radiation. Yarn composition, tightness of the weave, and dark colors increase a garment's UPF.

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