In a communication published in the journal Experimental Dermatology, Alan Verkman from the University of California questions the safety of a number of anti-ageing ingredients that upregulate the expression of the protein aquaporin-3 (AQP3). Protein facilitates water movement and 'moisturisation' AQP3 is a member of a family of membrane proteins called the aquaporins that play a role in water movement in and out of cells. AQP3 is the membrane protein found in human skin cells and it is thought to facilitate the movement of water and glycerol across skin cell membranes. This relationship between the expression of AQP3 and the water content or 'moisturisation' of the skin has prompted a number of companies to release ingredients that upregulate the expression of the membrane protein and thereby improve skin moisturisation. However, according to Verkman there may be an association between the epidermal expression of AQP3 and skin tumour formation. AQP3 expression and tumour formation? Human squamous cell carcinomas, the second most common form of skin cancer, strongly express the AQP3 protein, according to Verkman. In addition, mice lacking the AQP3 protein failed to form tumours whereas the wild-type mice (mice with the normal AQP3 gene) that underwent the same tumour-inducing conditions formed multiple tumours. Furthermore, in general the expression of the aquaporin proteins in tumour cells has been found to increase their migration, invasiveness and metastatic potential, according to the scientist, however, there is no data for the effect of AQP3 and the migration of skin cell tumours. At present the data is not sufficient to come to any concrete conclusions - the ability to prevent tumours by AQP3 deletion does not prove a link between the proteins' upregulation and skin tumour formation. However, according Verkman it is 'not unreasonable' to suggest a link and he advises caution in the use of such cosmetics. "Given the relationship between epidermal AQP3 expression and tumour cell proliferation, caution seems warranted in the use of cosmetics containing ingredients that increase epidermal AQP3 expression," he concludes. Furthermore, he proposes that further studies are needed to investigate the relationship between the use of such cosmetics and the incidence of skin cancers.