Scientists at Keele University in Staffordshire have questioned the safety of aluminium added to sunscreens and sunblocks.
The researchers, Scott Nicholson, BSc, and Dr Christopher Exley, PhD, Birchall Centre for Inorganic Chemistry and Materials Science at Keele, measured the aluminium content of sunscreens/sunblocks, which either include or do not include an aluminium salt (for example, aluminium hydroxide, aluminium oxide, aluminium silicate, aluminium stearate, aluminium starch octenylsuccinate) as an ingredient.
Aluminium was present in all seven products tested and its content was of particular significance in three products, each of which listed it as an ingredient. Following numerous enquiries the manufacturers were not forthcoming as to the role of aluminium in their product, except one manufacturer, who confirmed that aluminium hydroxide was added to their product to coat the surface and thereby prevent the agglomeration of another ingredient, titanium dioxide particles.
World Health Organisation guidelines recommend a single application of at least 35mL of a sunscreen/sunblock to achieve the stated sun protection factor. For three of the sunscreens/sunblocks investigated a single application of product would result in 200 mg of aluminium being applied to the skin surface. In addition, WHO guidelines suggest re-application of product every two hours which, for example, for an average day on the beach, would result in up to 1g of aluminium being applied to the skin surface.
Skin is permeable to aluminium salts when, for example, they are topically applied as antiperspirant formulations. It will accumulate in the skin and be transported to sites throughout the body. It is highly likely that the everyday use of sunscreens/sunblocks is an hitherto unrecognised contributor of aluminium to the human body burden of this non-essential metal. Perhaps of immediate significance is the potential for aluminium in the skin to act as a pro-oxidant.
Recent research in the journal Free Radical Biology and Medicine has shown that UV filters in sunscreens promote the formation of reactive oxygen species (ROS) in the nucleated epidermis of the skin. The authors speculate upon the role which might be played by anti-oxidants, either already in the skin or included in sunscreen formulations, in counteracting the pro-oxidant activities of UV filters though they did not consider how the presence of additional pro-oxidants might exacerbate such effects.
Aluminium is one such pro-oxidant and could significantly increase the potential for oxidative damage in the skin. While the relationship between the burgeoning use of sunscreens/sunblocks and the increased incidence of skin cancers and, in particular, melanoma, is highly controversial it has not hitherto been considered that aluminium in these products could be an extremely significant contributing factor. Of course, aluminium is already in the skin surface and may not need to be a component of sunscreens/sunblocks to exacerbate oxidative damage attributed to the application of such products.