The vulva is relatively insensitive to menses-induced irritation

Skin patch testing of menses and venous blood on the vulva (labia majora) and the upper arm was performed to assess the potential contribution of these biological fluids to vulvar irritation during menstruation. After 24 and 48 hours of occlusive exposure, the skin of the labia majora was relatively unaffected by these fluids compared to the skin of the upper arm: no significant irritation was observed on the labia at either exposure time, but discernible irritation was elicited on the upper arm after 48 hours of exposure. Pre-treatment of the upper arm with a petrolatum-based emollient attenuated the upper arm response. Semi-occlusive conditions also reduced the degree of upper-arm irritation elicited test materials and an irritant control, sodium lauryl sulfate. The relative insensitivity of the vulva to irritation by menses or blood was not predictable a priori because some irritants elicit heightened responses on the vulva relative to the arm (3). These results suggest that the vulva (labia majora) may be adapted to be less sensitive to menses-induced skin irritation than other anatomical sites.