Free Radical Biology & Medicine 43 (2007) 1216–1217www.elsevier.com/locate/freeradbiomed

Letter to the Editor

Aluminum:Apotential pro-oxidant in sunscreens/sunblocks?

Keywords: Aluminum; Pro-oxidant; Sunscreen; Sunblock; Skin cancer;Melanoma; Free radicals

To the Editor:

We have measured the aluminum content of sunscreens/sunblocks which either include or do not include an aluminumsalt (for example, aluminum hydroxide, aluminum oxide,aluminum silicate, aluminum stearate, aluminum starch octe-nylsuccinate) as an ingredient. Aluminum was present in allproducts (Table 1) and its content was of particular significance(N0.1% w/w) in three products, each of which listed it as aningredient. After numerous inquiries the manufacturers werenot forthcoming as to the role of aluminum in their product,except the manufacturer of Simple Sun Protection Cream, whoconfirmed that aluminum hydroxide was added to their productto coat the surface and thereby prevent the agglomeration ofanother ingredient, titanium dioxide particles. WHO guidelines[1] for the application of sunscreens/sunblocks recommend asingle application of at least 35 ml of product to achieve thestated sun protection factor (SPF). For three of the sunscreens/sunblocks investigated in this study a single application ofproduct would result in ca. 200 mg of aluminum being applied

Table 1The aluminum content of a range of commercially available sunscreens and theamount of aluminum which is applied to the skin from a single WHO-recommended application

Product % Aluminumw/w

Milligramsaluminum per35-ml application

Nivea Sun moisturizing sun lotion SPF 15 0.00015 0.25Hawaiian Tropic sun lotion SPF 15 0.00010 0.17Boots Soltan Kids a at SPF 30 0.00235 3.90Boots Soltan Kids a at SPF 50 0.00210 3.49Simple Sun Protection a cream SPF 50 N0.10 b N166.00Garnier Ambre Solaire a SPF 30 N0.10 b N166.00Piz Buin Mountain a SPF 50 N0.10 b N166.00

a An aluminum compound is listed by this product as an ingredient.b The aluminum content of this product was in excess of what could be

reliably measured using GFAAS.

0891-5849/$ - see front matter © 2007 Elsevier Inc. All rights reserved.doi:10.1016/j.freeradbiomed.2007.07.010

to the skin surface (Table 1). In addition, WHO guidelinessuggest reapplication of product every 2 h, which, for example,for an average day on the beach, would result in up to 1 g ofaluminum being applied to the skin surface. Skin is permeableto aluminum salts when, for example, they are topically appliedas antiperspirant formulations [2]. It will accumulate in the skinand it will be transported from the skin to systemic sites [3]. Itis highly likely that the everyday use of sunscreens/sunblocks isa hitherto unrecognized contributor of aluminum to the humanbody burden of this nonessential metal. Perhaps of immediatesignificance is the potential for aluminum in the skin to act as apro-oxidant [4]. Recent research in Free Radical Biology andMedicine has shown that UV filters in sunscreens promote theformation of reactive oxygen species in the nucleated epidermisof the skin [5]. The authors speculated upon the role whichmight be played by antioxidants, either already in the skin orincluded in sunscreen formulations, in counteracting the pro-oxidant activities of UV filters, though they did not considerhow the presence of additional pro-oxidants might exacerbatesuch effects. Aluminum is one such pro-oxidant and couldsignificantly increase the potential for oxidative damage in theskin [4,6]. Whereas the relationship between the burgeoninguse of sunscreens/sunblocks and the increased incidence ofskin cancers and, in particular, melanoma is highly controver-sial [5] it has not hitherto been considered that aluminum inthese products could be an extremely significant contributingfactor. Of course, aluminum is already in the skin surface andmay not need to be a component of sunscreens/sunblocks toexacerbate oxidative damage attributed to the application ofsuch products.

References

[1] World Health Organisation, Ultraviolet radiation and the INTERSUNProgramme. Online at http://www.who.int/uv/en/.

[2] Flarend, R.; Bin, T.; Elmore, D.; Hem, S. L. A preliminary study of thedermal absorption of aluminium from antiperspirants using aluminium-26.Food Chem. Toxicol. 39:163–168; 2001.

[3] Exley, C.; Burgess, E.; Day, J. P.; Jeffery, E. H.; Melethil, S.; Yokel,R. A. Aluminium toxicokinetics. J. Toxicol. Environ. Health 48:569–584;1996.

[4] Exley, C. The pro-oxidant activity of aluminum. Free Radic. Biol. Med.36:380–387; 2004.

[5] Hanson, K. M.; Gratton, E.; Bardeen, C. J. Sunscreen enhancement ofUV-induced reactive oxygen species in the skin. Free Radic. Biol. Med.41:1205–1212; 2006.

[6] Khan, A.; Dobson, J. P.; Exley, C. Redox cycling of iron by Aβ42. FreeRadic. Biol. Med. 40:557–569; 2006.

1217Letter to the Editor

Scott NicholsonChristopher Exley*

Birchall Centre for Inorganic Chemistry and Materials Science,Lennard-Jones Laboratories, Keele University,

Staffordshire ST5 5BG, UKE-mail address: c.exley@chem.keele.ac.uk.

*Corresponding author. Fax: +44 1782 712378.27 June 2007