A competent epidermal barrier is crucial for terrestrial mammals. This barrier must
keep in water and prevent entry of noxious stimuli. Most importantly, the epidermis must also
be a barrier to ultraviolet radiation (UVR) from the sunlight. Currently, the effects of ultraviolet
radiation on epidermal barrier function are poorly understood. However, studies in mice
and more limited work in humans suggest that the epidermal barrier becomes more permeable,
as measured by increased transepidermal water loss, in response UVR, at doses sufficiently
high to induce erythema. The mechanisms may include disturbance in the organisation
of lipids in the stratum corneum (the outermost layer of the epidermis) and reduction in tight
junction function in the granular layer (the first living layer of the skin). By contrast,
suberythemal doses of UVR appear to have positive effects on epidermal barrier function.
Topical sunscreens have direct and indirect protective effects on the barrier through their ability
to block UV and also due to their moisturising or occlusive effects, which trap water in the
skin, respectively. Some topical agents such as specific botanical extracts have been shown to
prevent the loss of water associated with high doses of UVR.
In this review, we discuss the current literature and suggest that the biology of UVR-induced
barrier dysfunction, and the use of topical products to protect the barrier, are areas worthy of