According to the symptoms you describe (red spots and irritation when exposed to sun) you are probably experiencing some kind of photodermatosis. There are several types of photodermatoses:


1. Photo-TRAUMATIC dermatoses. This condition is due to the direct physical action of sunlight on the skin. It depends upon the combintation of 3 factors: genetically determined skin type, sunlight strength and duration of exposure. Acute affection can cause inflammation (dermatitis solaris); chronic affection can cause degeneration of the skin;


2. Photo-TOXIC dermatoses. This condition is attributed to the common action of sunlight in combination with a photo-sensibilizating substance applied locally to the skin. Sensibilization in this case is not an allergic reaction (there are no immunological mechanisms present). For example, berloque dermatitis (when the substance is cosmetics) and phytophotodermatitis (when the substance is a plant derivitative) belong to this group.


3. Photo-ALLERGIC dermatoses. In this case, immunological mechanisms (allergic reaction) are included in the pathogenesis in combination with the presence of sunlight and a photosenzibilizator. Photoalergic dermatitis in its acute form is a part of this group of dermatoses. The photosensibilizating substance (allergen) first stimulates an immunologicaly sensitive reaction in the body (allergy). Then, the next contact with the particular substance sunlight, can cause skin lesions to occur. Contact with the allergen can happen through the skin, through food, or by injection;


4. DYSMETABOLIC photodermatoses. This type of dermatosis can be caused by an enzyme deficit due to a genetic defect (like porphyries), or lack of a particular vitamin (pellagra for instance);


5. Photodermatoses can exist with unknown etiologies. The most common type of unknown dermatosis is called "polymorphic light eruption." This condition stimulates immunological mechanisms but an allergen is not indentified. Urticaria solaris and hidroa aestvalia are other representatives from this group.


You can request photo-epicutaneus tests to identify possible photosensibilizating substances (allergen). Treatment always includes avoiding both the allergen (if found) and sunlight. You can consult a dermatologist about further diagnostic and therapeutic procedures.