Skin disorders caused by exposure to sunlight are called photodermatoses. The solar radiation reaching the surface of the Earth is divided into infrared light, visible light and ultraviolet radiation. Ultraviolet or UV radiation is responsible for most harmful skin lesions. One should consider photodermatoses: * if patient tells us that skin lesions developed after sun exposure * if we see that lesions have a typical distribution on the body parts that are exposed to sunlight, so called photoexposed regions * if itching or skin lesions occur every time after sun exposure. These conditions may be caused by direct harmful effects of UV radiation on the skin, as in case of sunburn, they may occur as a part of some systemic diseases, such as systemic lupus erythematosus, porphyria, they may be a result of allergic reaction, or of intake some medications that increase the skin sensitivity to solar radiation. There are a number of photodermatoses whose cause is unknown, such as polymorphic light eruption, actinic prurigo, hydroa vacciniforme, chronic actinic dermatitis and solar urticaria.

Sunburn — dermatitis solaris

Skin lesions occur after intense sun exposure, usually within 2 to 6 hours, with most pronounced problems after 24 hours. Parts of the skin that have been exposed to the sun become intensively red, swollen, hot, and then blisters appear. A person usually has an intense burning sensation, accompanied by malaise, fever and headache. After a couple of days, the blisters break, leaving behind areas with peeled skin. Recommended treatment consists of the use hydrophilic creams, topical corticosteroid preparations and compresses with saline. In severe conditions, bed rest in darkness, intake of plenty of fluids and possibly systemic antihistamines are recommended.

Polymorphic light eruption

It is a common condition especially in younger people, a few hours after exposure to sunlight or artificial sources of UV radiation (tanning beds). It usually occurs during spring or at the beginning of summer, only to resolve in autumn and winter. Lesions in the form of red papules and plaques are spread across sun exposed body parts, especially on the neck, extensor surfaces of the arms and hands, although they can also affect larger skin areas. The face is usually spared. Patients complain of itching with lesser or greater intensity. Over time, the lesions gradually recede. The disease can occur over several years, with periods of when the condition recedes during the colder months. Polymorphic light eruption treatment primarily involves photoprotection, i.e. adequate protection from the sun by using protective creams and preparations with SPF 50, wearing of protective clothing and avoiding sun exposure. In case of more pronounced lesions, topical and systemic corticosteroid preparations are administered.

Actinic prurigo

Lesions occur as early as in childhood and in most people recede in the period of adolescence. There is a genetic predisposition to the development of this condition. On sun exposed body parts like the face, upper arms and less frequently on covered body parts, red papules and tiny nodules appear that are often moist with scabs on the surface. Long-term cheilitis (inflammation of the lips) and conjunctivitis can be often seen. Lesions are accompanied by an intense itching and scratching marks. Occasionally, patches of thickened skin are present, resembling atopic dermatitis. During the winter months lesions usually recede. Actinic prurigo treatment involves strict photoprotection by avoiding sun exposure and use of protective creams. It is recommended to use creams based on corticosteroids or immunomodulatory preparations (tacrolimus and pimecrolimus). In severe forms of the disease, narrowband UVB therapy, systemic corticosteroids, thalidomide, azathioprine and cyclosporine may be used.

Solar urticaria

Solar urticaria occurs relatively rarely. It belongs to the group of physical urticarias that are the result of sun exposure. A few minutes after sun exposure, the skin swells and pale red plaques appear especially on the upper part of the trunk and on the hands, accompanied by the feeling of itching, burning or rarely pain. Other problems such as weakness, dizziness, headache, nausea or shortness of breath are also present although less frequently. After one to two hours the lesions resolve spontaneously. In a certain number of people, occasional and prolonged sun exposure can lead to the reduction and resolution of the disease. Spontaneous resolution of the disease is also observed in about 15% of people after 5 years. It should be noted that in a certain number of people who use chlorpromazine or tetracyclines in therapy for other diseases, solar urticaria may occur, which is referred to as drug-induced solar urticaria. Photoprotection is very important part of the treatment. In addition, antihistamines should be used, usually one hour before the intended sun exposure. In a certain number of patients, gradual exposure to UVA or PUVA therapy can lead to the resolution of solar urticaria.

Hydroa vacciniforme

It is a rare form of photodermatosis. It occurs in childhood and usually resolves during adolescence. It is characterised by the appearance of reddish papules (pimples) and plaques. After a few days, small fluid-filled blisters develop that heal with pox-like scars. Lesions are present on parts of the body that are exposed to sunlight, especially on the face and upper limbs and back of the hands. Hydroa vacciniforme is very resistant to treatment. It is recommended to strictly avoid sun exposure by applying photoprotective creams and measures. The use of narrowband and wideband UVB therapy, PUVA, antimalarial medications, azathioprine, thalidomide and cyclosporine, beta carotene, and fish oil in the treatment has shown questionable results.

Chronic actinic dermatitis

This type of condition occurs in elderly people, more often in men. It affects photo-exposed parts of the body, especially the face and neck. Ultraviolet radiation and less visible light are the main causative agents of this condition, so it is regarded as a type of contact allergic reaction. Lesions can occur in people who have not previously been ill, as well as in people who have had a contact allergic reaction to various allergens from the environment or in people who use medications that increase the sensitivity of the skin to the sun. Very often allergic reactions to odours, topical drugs or plant allergens are present. Reddish papules, plaques, inflammatory lesions that can be acute and chronic course develop on the sun exposed body parts. Due to the intensive itching and scratching, patches of thickened skin gradually develop. These individuals periodically also have eczema lesions on the palms and soles. The time period of resolution of lesions can vary a lot. In about 20% of people the condition recedes in a period of 10 years. The prevention is extremely important in therapy, in terms of strict avoidance of sun exposure, as well as contact with allergens from the environment. Periodically, corticosteroid creams or local immunomodulators (tacrolimus, pimecrolimus) are used in therapy. Regular use of emollients and photoprotective creams preparations is recommended. With prolonged and resistant forms of the disease, treatment with PUVA therapy, systemic corticosteroids, cyclosporine or azathioprine is also advised.

Phototoxic dermatitis

It occurs as a result of sun exposure in people who have previously been in contact with certain substances that increase the skin sensitivity to the sun (so-called photosensitisers). Plants that most often increase the sensitivity of the skin to ultraviolet radiation are parsley, celery, figs and lemon, as they contain furocoumarins, psoralen and various essential oils. Similar effects are observed in tar and some drugs that are used orally (sulfonamides, tetracyclines, phenothiazine, nalidixic acid). Upon contact with external allergens, usually in a period of 24h, redness, swelling and small or larger blisters develop. Lesions are most often accompanied by pain — burning or itching sensations. After the lesions recede, brownish spots appear. This type of lesion most often occurs in people who are in contact with different plants, during the work in agricultural field or during the stay in nature. Phototoxic dermatitis treatment is carried out by applying compresses made of saline and corticosteroid creams. It is advised to avoid contact with plants that are known photosensitisers.
Svetlana Đurišić specijalista dermatovenerologije

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