A rash or itching after sun exposure is a common cause of concern, and doctors describe such reactions as photodermatoses. In everyday speech, these reactions are called sun allergy. Let us look at what lies behind this name.
What sun allergy and photodermatosis are
Photodermatosis (Greek phos, photos — light, derma — skin) is defined as a non-inflammatory skin process due to increased skin sensitivity to sunlight; the same phenomena are called light diseases or actinodermatoses.
Polymorphic light eruption and other types of reactions to light
Polymorphic light eruption is the most common type of photodermatosis: it occurs in about 10% of the population, appears in spring and resolves in late summer.
In M. A. Shteinberg's classification (1958), true photodermatoses include solar prurigo, solar dermatitis, solar eczema, light pox, cutaneous porphyria and actinic cheilitis; relative forms in chemical industry workers are distinguished separately.
Phototraumatic reaction, or solar dermatitis, occurs in any person after prolonged exposure to scorching sun: the acute form is a burn with redness and blisters, the chronic form is skin thickening with folds and spider veins.
Why a reaction to ultraviolet occurs
Ultraviolet rays are an invisible form of radiation that passes through the skin and damages cells; tanning and sunburn are signs of such damage. Photodermatosis is caused by rays in the 320–400 nm range and visible light at 400–800 nm. A reaction is more likely with the first strong dose after a long time — in spring, in early summer, on a trip to a sunny country; as summer progresses, the skin adapts and the rash appears less often.
Sensitivity is increased by tetracyclines, phenothiazines, furosemide, nonsteroidal anti-inflammatory drugs, as well as the sap of plants containing furocoumarins — angelica, Sosnowsky's hogweed, parsnip, and common rue in Crimea.
How sun allergy manifests on the face, hands and body
The main sign is a rash several hours or days after sun exposure: small raised spots or vesicles, sometimes large patchy areas; the skin becomes pink or red, which is harder to notice on brown and black skin, and the rash itself itches or burns.
The location suggests the mechanism: on the arms, legs and chest — areas usually covered by clothing — the rash occurs more often, whereas on the face and neck the exposed areas are affected, while the skin behind the ears and under the chin is protected. A special variant is juvenile spring eruption with itchy vesicles on the ears. There may also be hyperpigmented spots that do not fade on pressure; if sun is avoided, the rash resolves in about a week.
Sun allergy in children and adults
Polymorphic light eruption is more common in people under 40 years of age, in women and in people with white skin; in boys aged 5–14 years, juvenile spring eruption with ear involvement is more common.
In those who constantly work in the open sun, chronic changes begin on the face and neck: persistent tanning, skin thickening, folds. Ultraviolet is harmful at any time of year and at any temperature, and a tan is not a sign of health.
How to distinguish it from other causes of rash and when to see a doctor
Polymorphic light eruption may resemble heat rash, so a doctor's examination helps to distinguish them. If in doubt, the doctor assesses the rash and, if necessary, refers to a dermatologist.
An appointment is needed if at least one of the reasons listed below appears.
- The rash worsens or does not resolve in about a week if sun is avoided.
- Swelling has appeared in the area of the rash.
- There is joint and muscle pain or unusual fatigue.
A sun rash by itself is not a reason to call an ambulance; 103/112 — for a life-threatening condition, for example a sudden sharp deterioration in well-being.
The reference text explains the mechanism and the limits of normal, but does not replace an examination: the approach is determined by the doctor.
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This content is for reference and does not replace a doctor's consultation. Medical disclaimer