Background: Nowadays skin damages caused by ultraviolet (U.V.) radiation from the sun were increased; accordingly necessity for safe and inexpensive protective products for reducing the harmful effects of this ray is unassailable. The antiradical, anti irritation and anti-cancer properties of silymarin make it a suitable option for use in cream formulation to investigate its effect on skin disorders caused by U.V. radiation. In this research effect of local application of a cream containing silymarin in prevention of the harmful effects of U.V. radiation on the guinea pig skin were studied and evaluated by using histopathologic and clinical findings.

Methods: 75 albino guinea pigs were randomly divided into five groups of fifteens. 2cm2 of the back hair was shaven. In the first group no treatment was applied, in the second group vaseline, in group 3 base cream without silymarin extract, in group 4 silymarin extract and in group 5 cream containing silymarin extract were used.

Results: In clinical assessment, skin scaling, skin irregularity, erythema, skin hyperpigmentation, and edema were observed and in histopathological observation epidermal hyper keratosis, hyperpigmentation, exocytosis, acanthosis, chromatin discoloration in nucleus of epidermal squamous cells, perifolliculitis, dermal vascular hyperemia, edema and dermal thickness, infiltration of plasma cell lymphocytes and eosinophyls into dermis were detected. The statistical comparison of group 1 and group 5 shows statistically significant difference in most indices (p<0.01).

Conclusions: Clinical and histopathologic examinations showed that local application of a cream containing silymarin is effective in prevention of skin damage caused by U.V. radiation in guinea pig's skin; also the results of the clinical and histopathologic observation in this study confirm the enzymatic results in other researches.