الفهرس 
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Abstract
One of the most important functions of the skin is protection against ultraviolet rays, which is accomplished through melanin secretion.
Histamine is a well-known inflammatory and allergic mediator, but its role in melanogenesis is still under research.
In the present work, 50 guinea pigs were exposed to narrow band ultraviolet B (NB-UVB). Hair was shaved from (4)areason the dorsal skin of each animal. During the course of irradiation, the four shaved areas of the skin was treated as follows:
Area 1:remains unprotected from NB-UVB(control).
Area 2: treated with a topical H1 antagonist (2% pheniramine in vaseline)twice daily.
Area 3:treated with a topical second generation H1 antagonist(2% fexofenadine in vaseline)twice daily.
Area 4: treated with a topical H2 antagonist(2% famotidine in vaseline)twice daily.
The study showed that the skin areas treated with pheniramine and fexofenadine, were darkened nearly to same extent as the control, while the area treated with famotidine exhibits little darkening.
These results suggest that histamine has a role in NB-UVB induced melanogenesis and that this role is mediated via H2 receptors (because its effect was blocked only by the H2 antagonist,famotidine)