DNC News

Sunscreens and bug repellent do not mix

Jacob Schor, ND

May 6, 2007

Subject: Sunscreens transport the pesticides contained in insect repellent into the blood stream

The chemicals used in sunscreen are absorbed through the skin and into your blood and are then excreted in your urine. [i] As sunscreens penetrate the skin, they help carry other chemicals that are on the skin into the body. Examples of chemicals transported through the skin include pesticides, [ii] herbicides, [iii] [iv] and insect repellents.

Sunscreens increase absorption of DEET containing insect repellents through the skin. [v]

You should never use sunscreen on your skin the same time you are using DEET containing insect repellents.

I've told patients that, ‘At least sunscreen keeps us from getting sun burned.'

This might have been a dumb thing to say. Sunscreens prevent reddening of the skin by blocking an enzyme in the skin that makes nitric acid. One function of nitric acid is to inflame the skin. This inflammation signals your immune system to start protecting your skin and the pain tells you to get out of the sun. When sunscreens block nitric acid formation, the skin doesn't redden, you stay in the sun longer, your skin is more damaged, and you increase your risk of skin cancer and premature aging. [vi] By preventing nitric acid formation, sunscreens only prevent the skin from getting red, they do not necessarily prevent sun damage.

With this in mind, we'll try to remember to reorder the DEET-Free insect repellent we've been stocking the last few summers.

Past newsletters provide info on these repellents:

Natural Insect Repellent May 2004 http://denvernaturopathic.com/news/DEETFree.html

Natural Mosquito repellents, West Nile Virus, Tumor Necrosis Factor and other related topics July 2006 http://denvernaturopathic.com/news/westnile.html

[i]

 
Comment in:

•  J Invest Dermatol. 2004 Jul;123(1):xi-xii.

Systemic absorption of the sunscreens benzophenone-3, octyl-methoxycinnamate, and 3-(4-methyl-benzylidene) camphor after whole-body topical application and reproductive hormone levels in humans.

Janjua NR , Mogensen B , Andersson AM , Petersen JH , Henriksen M , Skakkebaek NE , Wulf HC .

Department of Dermatology, Bispebjerg Hospital , Copenhagen , Denmark . NRJ01@bbh.hosp.dk

Recent in vitro and animal studies have reported estrogen-like activity of chemicals used in sunscreen preparations. We investigated whether the three sunscreens benzophenone-3 (BP-3), octyl-methoxycinnamate (OMC), and 3-(4-methylbenzylidene) camphor (4-MBC) were absorbed and influenced endogenous reproductive hormone levels in humans after topical application. In this 2-wk single-blinded study 32 healthy volunteers, 15 young males and 17 postmenopausal females, were assigned to daily whole-body topical application of 2 mg per cm(2) of basic cream formulation without (week 1) and with (week 2) the three sunscreens at 10% (wt/wt) of each. Maximum plasma concentrations were 200 ng per mL BP-3, 20 ng per mL 4-MBC, and 10 ng per mL OMC for females and 300 ng per mL BP-3, 20 ng per mL 4-MBC, and 20 ng per mL OMC for men. All three sunscreens were detectable in urine. The reproductive hormones FSH, LH were unchanged but minor differences in testosterone levels were observed between the 2 wk. A minor difference in serum estradiol and inhibin B levels were observed in men only. These differences in hormone levels were not related to sunscreen exposure.

[ii]

 
Sunscreens containing physical UV blockers can increase transdermal absorption of pesticides.

Brand RM , Pike J , Wilson RM , Charron AR .

Department of Internal Medicine, Evanston Northwestern Healthcare and Feinberg School of Medicine at Northwestern University, Evanston , IL 60201 , USA . rhbrand@enh.org

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 (P<0.05). Transdermal studies using paraquat, parathion and malathion pretreated with a representative sunscreen all demonstrated significant penetration enhancement when compared to controls (P<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 UV absorbers 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.

[iii]

 
Effects of active sunscreen ingredient combinations on the topical penetration of the herbicide 2,4-dichlorophenoxyacetic acid.

Pont AR , Charron AR , Wilson RM , Brand RM .

Department of Internal Medicine, Evanston Northwestern Healthcare and Feinberg School of Medicine at Northwestern University, Evanston , IL 60201 , USA .

Sunscreen use can reduce the incidence of certain skin cancers. However, a number of commercially available formulations have been shown to enhance the transdermal penetration of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). Most of the active ingredients used in these compounds can individually act as penetration enhancers. Commercial sunscreens frequently contain multiple active ingredients in order to provide broad sunscreen protection. The purpose of this study was therefore to examine the effect of these active ingredient combinations on the transdermal absorption of 2,4-D in vitro. All six of the combinations tested resulted in increased cumulative penetration (P <0.01) and faster lag times (P <0.05). The 2,4-D cumulative penetration in the presence of the OFF! Deepwoods combination was significantly greater than the absorption with either the individual ingredients or their average (P <0.05). A systematic study designed to isolate the chemicals responsible for this enhancement demonstrated that with UV absorbers DEET synergistically increased the 2,4-D penetration and that DEET's cumulative enhancement properties correlate with its concentration. By contrast, octocrylene significantly slowed the lag time when used in combinations and was the only active ingredient that showed any antagonistic effects on 2,4-D penetration. Because none of the active ingredient combinations were able to inhibit dermal uptake of 2,4-D, it seems that proper selection of inert ingredients may be the most feasible solution for reducing penetration enhancement.

PMID: 15462531 [Pu

[iv]

 
Active ingredients in sunscreens act as topical penetration enhancers for the herbicide 2,4-dichlorophenoxyacetic acid.

Pont AR , Charron AR , Brand RM .

Department of Biological Systems Engineering, University of Nebraska-Lincoln , Lincoln , NE 68583 , USA .

Agricultural workers are encouraged to use sunscreen to decrease the risk of UV-related skin cancer. Our previous studies have shown certain commercial sunscreens to be penetration enhancers. The focus of this project is to determine whether active ingredients in sunscreen formulations (i.e., the UV absorbing components and insect repellants for the sunscreen/bug repellant combinations) also act as dermal penetration enhancers for herbicides in vitro. The total percentages of 2,4-dichlorophenoxyacetic acid (2,4-D) penetrating through hairless mouse skin in 24 h ranged from 54.9 +/- 4.7 for the no sunscreen control to 86.9 +/- 2.5 for padimate-o. Of the active ingredients tested (7.5% octyl methoxycinnamate, 7% octocrylene, 0.6% oxybenzone, 5% homosalate, 5% octyl salicylate, 8% padimate-o, 10% sulisobenzone, and 9.5% and 19% N,N-diethyl-m-toluamide [DEET]), all but octocrylene led to a significant increase in total 2,4-D penetration as compared to the control (P < 0.05), and only octocrylene and oxybenzone did not significantly decrease the corresponding lag time. Octyl salicylate (P < 0.01) and octyl methoxycinnimate (P < 0.05) significantly increased the 3H2O penetration across mouse skin, indicating physical damage to the stratum corneum. Additional studies demonstrated that the penetration enhancement seen across hairless mouse skin also occurred with human skin. Thus, the active ingredients of sunscreen formulations enhance dermal penetration of the moderately lipophilic herbicide 2,4-D.

PMID: 15020197 [PubMed - indexed for MEDL

[v]

 
Active ingredients in sunscreens act as topical penetration enhancers for the herbicide 2,4-dichlorophenoxyacetic acid.

Pont AR , Charron AR , Brand RM .

Department of Biological Systems Engineering, University of Nebraska-Lincoln , Lincoln , NE 68583 , USA .

Agricultural workers are encouraged to use sunscreen to decrease the risk of UV-related skin cancer. Our previous studies have shown certain commercial sunscreens to be penetration enhancers. The focus of this project is to determine whether active ingredients in sunscreen formulations (i.e., the UV absorbing components and insect repellants for the sunscreen/bug repellant combinations) also act as dermal penetration enhancers for herbicides in vitro. The total percentages of 2,4-dichlorophenoxyacetic acid (2,4-D) penetrating through hairless mouse skin in 24 h ranged from 54.9 +/- 4.7 for the no sunscreen control to 86.9 +/- 2.5 for padimate-o. Of the active ingredients tested (7.5% octyl methoxycinnamate, 7% octocrylene, 0.6% oxybenzone, 5% homosalate, 5% octyl salicylate, 8% padimate-o, 10% sulisobenzone, and 9.5% and 19% N,N-diethyl-m-toluamide [DEET]), all but octocrylene led to a significant increase in total 2,4-D penetration as compared to the control (P < 0.05), and only octocrylene and oxybenzone did not significantly decrease the corresponding lag time. Octyl salicylate (P < 0.01) and octyl methoxycinnimate (P < 0.05) significantly increased the 3H2O penetration across mouse skin, indicating physical damage to the stratum corneum. Additional studies demonstrated that the penetration enhancement seen across hairless mouse skin also occurred with human skin. Thus, the active ingredients of sunscreen formulations enhance dermal penetration of the moderately lipophilic herbicide 2,4-D.

PMID: 15020197 [PubMed - indexed for MEDL

[vi]

 
Sunscreen ingredients inhibit inducible nitric oxide synthase (iNOS): a possible biochemical explanation for the sunscreen melanoma controversy.

Chiang TM , Sayre RM , Dowdy JC , Wilkin NK , Rosenberg EW .

Department of Medicine (Rheumatology) and Molecular Sciences bResearch Services, VA Medical Center, Memphis , TN 38088-1342 , USA .

Sunscreen products are rated upon their ability to inhibit visible redness of the skin 24 h after measured doses of ultraviolet (UV) exposure (Sun Protection Factor, SPF). Although sunscreens prevent UV-induced redness, their ability to protect against melanoma or the development of moles is less clear. UV-induced redness occurs in part by the action of nitric oxide (NO), synthesized in the skin. NO is also an important immunoregulatory molecule in the induction of the cell-mediated tumour immune response. In this study, various sunscreen ingredients were tested for their ability to inhibit the production of NO. Four of the five sunscreens tested directly inhibited the conversion of arginine to citrulline by inducible nitric oxide synthase (iNOS) in vitro. These findings suggest that sunscreens may prevent redness partly by UV absorption and partly by inhibition of the skin's inflammatory response. As such, sunscreens might promote instead of protect against melanoma.

PMID: 15714114 [PubMed - indexed for MEDLINE]