Classical burning
The sun's rays contain ultraviolet A and B rays (UVA and UVB), which can damage the skin. For longer and unprotected exposure to the sun strikes the human large number of these rays, which can lead to sunburn, changes in its structure as well as cancer.
Sun allergen
Solar radiation but may cause difficulties with anyone, irrespective of its amount, already after the "low doses". Allergy to sunlight in fact not an allergic reaction, but has a common name histamine release substances into the blood. The results are manifestations that appear on parts of the body exposed to sunlight, usually in the neck, face or hands: Redness of the skin , itching, formation of buds - hives, blisters.
Phototoxic reactions
This inconvenience may occur in the following cases:
after the use of anti-inflammatory preparations (containing the active substance ketoprofen)
when taking antibiotics (sulfonamides, cotrimoxazole, doxycycline)
after the consumption of certain foods, such as celery and citrus fruits,
the same effects can be even cosmetics, soaps and sunscreens.
For phototoxic reaction severity of allergy directly dependent on the length LOCATION. The amount of radiation necessary to rash broke, but differs from case to case.
Photosensitivity
This undesired response of the organism occurs even in certain diseases. A typical example is the butterfly rash on the face (both cheeks reddening associated strip across the bridge of the nose in the shape of a butterfly's wings) in the name of autoimmune disease lupus. Increased sensitivity to the sun's rays are also characterized by a rare, inherited metabolic disorder called porphyria.
Especially if you are taking medicines which are phototoxicity occurs, avoid direct sunlight. Between the 11th and 15th hour rather not go outside or be in the shade and protected with sunscreen and appropriate clothing.
Source: No alergie.cz