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157866 
Journal Article 
Sunscreens containing physical UV blockers can increase transdermal absorption of pesticides 
Brand, RM; Pike, J; Wilson, RM; Charron, AR 
2003 
1 
Toxicology and Industrial Health
ISSN: 0748-2337
EISSN: 1477-0393 
19 
1 
9-16 
English 
15462532 
WOS:000223255200002 
People are encouraged to wear sunscreens because of their effectiveness at reducing the risk of skin
cancer. The dermal penetration of the herbicide 2,4-D can be enhanced by commercial formulations
containing chemical ultraviolet (UV) absorbers, the absorbers themselves and the insect repellent
DEET. This work has been extended to determine whether commercially available sunscreens
containing the physical UV absorbers titanium dioxide (TiO2) or zinc oxide (ZnO) enhance the
transdermal absorption of pesticides. Hairless mouse skin was pretreated with either commercially
available sunscreens or the UV absorbers themselves, dissolved in phenyl trimethicone. In vitro
permeability studies were performed with the pesticides 2,4-D, paraquat, parathion or malathion.
The data demonstrate that pretreatment with five of the nine sunscreens tested increased the
transdermal absorption of 2,4-D (PB/0.05). Transdermal studies using paraquat, parathion and
malathion pretreated with a representative sunscreen all demonstrated significant penetration
enhancement when compared to controls (PB/0.05). Repeated 2,4-D and sunscreen applications
resulted in either no change between pulses or an increase in absorption after the second pulse
depending on the washing regimen. Examining penetration of individual UVabsorbers formulated in
phenyl trimethicone showed that that ZnO can impede 2,4-D penetration and TiO2 had no effect.
Combining UV absorbers in the presence of trimethicone resulted in ‘sunscreens’ that could actually
inhibit 2,4-D penetration. Inert ingredients therefore control the increased absorption seen in
commercial sunscreen products and this enhancement can be eliminated by substituting phenyl
trimethicone as the solvent. Sunscreen use must still be encouraged even with the undesirable side
effect of increased penetration through the skin. 
Multiple applications; pesticides; sunscreens; transdermal; UV absorbers