Laser-induced weal and flare reactions: clinical aspects and pharmacological modulation

Among the adverse effects of cutaneous laser therapy, weal and flare reactions immediately after treatment have received little attention, and the pathomechanisms are unclear.

To study clinical features and possible mechanisms of laser-induced weal and flare reactions in order to identify means of possible therapeutic intervention.

Normal skin from the inner arm of 20 volunteers was treated with an argon laser, and the size of weal and flare reactions was measured over a 60-min period. Skin biopsies were taken from four volunteers before and up to 24 h after laser treatment and examined histologically and immunohistologically. Possible underlying mechanisms were also explored using various topical or systemic pharmacological agents.

Wealing was noted in 19 of 20, and flare reactions in all volunteers, with peak values at 15 min. Skin biopsies showed central coagulation of the tissue, cleft formation between epidermis and dermis, normal numbers of morphologically intact mast cells on toluidine blue staining close to the lesion, and only minor upregulation of endothelial and leucocyte adhesion molecules. In agreement with these findings, pretreatment with acetylsalicylic acid, the H1-blocker loratadine and triamcinolone cream was ineffective or resulted in a non-significant reduction of weal and flare reactions. In contrast, local anaesthetics as well as neuropeptide depletion of skin with capsaicin abolished the reactions almost completely.

Transient weal and flare reactions in response to laser treatment occur in almost all persons and are based primarily on a neurogenic rather than a histamine- or mast cell-dependent mechanism.