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Biology 103
2002 First Paper
On Serendip

Chemical Sunscreens - When Are We Safe?

Virginia Culler

     The debate between chemical vs. physical sunscreens has been a hot one amongst the scientific community for a number of years. Since we became aware of the link between the sun and skin cancer, the rates for cases of melanoma have been on the rise, more so every year (1), most likely due to environmental factors (bigger hole in the ozone, pollution, etc.), overexposure to the sun, and improper protection precautions. While some scientists argue that there is no relationship between sunscreen use and the development of melanoma skin cancer (2 and 10), most of the scientific community agrees that sunscreen can be a (not THE) form of protection and prevention for all types of skin cancers.
     Given this sunscreen-based philosophy, we come to the question of what types of sunscreens are most effective at protecting us from the sun's harmful rays. To do this we must first analyze the types of UV (ultra violet) rays that the sun produces. Hans R. Larsen, MSc ChE, of International Health News, writes:
UVA rays constitute 90-95% of the ultraviolet light reaching the earth. They have a relatively long wavelength (320-400 nm) and are not absorbed by the ozone layer. UVA light penetrates the furthest into the skin and is involved in the initial stages of suntanning. UVA tends to suppress the immune function and is implicated in premature aging of the skin(2,13,14). UVB rays are partially absorbed by the ozone layer and have a medium wavelength (290-320 nm). They do not penetrate the skin as far as the UVA rays do and are the primary cause of sunburn. They are also responsible for most of the tissue damage which results in wrinkles and aging of the skin and are implicated in cataract formation. UVC rays have the shortest wavelength (below 290 nm) and are almost totally absorbed by the ozone layer. As the ozone layer thins UVC rays may begin to contribute to sunburning and premature aging of the skin. All forms of ultraviolet radiation are believed to contribute to the development of skin cancer.i
     In order to be fully effective at preventing skin cancer, then, sunscreens nowadays should offer broad spectrum protection (against both UVA and UVB rays). However, many ingredients in sunscreens are less effective than they claim at preventing skin cancer (5), as well as having other possibly harmful side effects (4). Therefore, we must pay more attention to the specific ingredients in our sun care products to effectively protect ourselves against skin cancer, something the FDA often doesn't tell us (6), at least not explicitly on the product packaging (4).
     The important distinction I want to look at is that of physical vs. chemical sunscreens. Chemical sunscreens work by absorbing the UV rays that hit them and therefore absorbing the radiation. Physical sunscreens, on the other hand, work by reflecting and/or scattering UV rays and radiation (5). The following chart (5) provides information about how each type of sunscreen performs:

(Parsol 1789)
(para-aminobenzoic acid)
(Octyl dimethyl paba)
Titanium Dioxide
Zinc oxide
(including transparent)

     From this chart alone, one might glean that physical sunscreens are more effective at overall sun protection. We see through the majority of studies that this is true (7,8). Furthermore, there is frightening evidence that these chemical sunscreens, as well as being less effective than their physical counterparts, are in fact somewhat harmful to us, and have even been argued to be the cause of interference with normal sexual development as well as other potential health problems (9 and 4, respectively). However, physical sunscreens have also been demonstrated to be both possibly harmful (11) and less effective in some cases than chemical sunscreens (12, 13). Therefore, it is difficult to analyze these sunscreens in a context of which is better/healthier or more effective, since it seems that both have been shown to have possible health side effects as well as flaws in efficiency. However, in one study it was shown that subjects were more likely to apply "about two-thirds the quantity of physical compared with chemical sunscreen. This reduction in amount applied is likely to lead, in practice, to the physical sunscreen providing a SPF of about one-half of that achieved with the chemical sunscreen" (14). This might indicate that, at least in practice, physical sunscreens are more effective than they are given credit for simply due to common misuse, and furthermore that, when used properly, physical sunscreens are just as if not more effective than chemical ones.
     Another point in favor of physical sunscreens is that countries around the world approve of their use in sunscreens, whereas only one chemical sunscreen is legal in Europe and commonly used in Canada and Australia (4)ii. Also, I was unable to find many resources stating that physical sunscreens had harmful effects similar to those of chemical sunscreens only one source claims anything of the sort, and it merely states that titanium dioxide (a physical sunscreen) is a compound "whose toxicity remains unclear" and whose "full effects on human health are still under investigation" (11). The same source also quotes the U.S. government's National Institute for Occupational Safety and Health (NIOSH) as labeling the chemical "a potential occupational carcinogen." However, these findings are less conclusive than any I found against physical sunscreens, and I am therefore inclined to trust chemical sunscreens more, at least until more information is available.

i Entire quote taken directly from (3) However, other sources indicate that UVC waves do not easily reach the earth's surface and are therefore not accounted for by most sunscreens.

ii However, source (4) also states the following in relation to this chemical:     In 1997, Europe, Canada, and Australia changed sunscreens to use three specific active sunscreen ingredients - avobenzone (also known as Parsol 1789), titanium dioxide, and zinc oxide - as the basis of sunscreens. In the USA, the cosmetic companies have held off this policy as they try to sell off their stockpiles of cosmetics containing toxic sunscreens banned in other countries. However, avobenzone is a powerful free radical generator and also should have been banned. Avobenzone is easily absorbed through the epidermis and is still a chemical that absorbs ultraviolet radiation energy. Since it cannot destroy this energy, it has to convert the light energy into chemical energy, which is normally released as free radicals. While it blocks long-wave UVA, it does not effectively UVB or short-wave UVA radiation, and is usually combined with other sunscreen chemicals to produce a "broad-spectrum" product. In sunlight, avobenzone degrades and becomes ineffective within about 1 hour.


1)Does sunscreen increase or decrease melanoma risk? Cancer HealthLINK
2)March 6, 1998, Hour 2: Sunscreen and Skin Cancer
3)Sun Screens and Cancer
4)The Chemical Sunscreen Health Disaster
5)ASPA Sun Safe Products / Sunscreen
6)No Title [FDA Regulations regarding sunscreen](this site takes a long time to load, please be patient)
7) Van Der Molen, RG; Hurks, HMH; Out-Luiting, C; Spies, F; Van't Noordende, JM; Koerten, HK; Mommaas, AM; "Efficacy of micronized titanium dioxide-containing compounds in protection against UVB-induced immunosuppression in humans in vivo," Journal of Photochemistry and Photobiology B: Biology [J. Photochem. Photobiol. B]. Vol. 44, no. 2, pp. 143-150. 10 Jul 1998.
8) Wolf, P; Donawho, CK; Kripke, ML; "Effect of sunscreens on UV radiation-induced enhancement of melanoma growth in mice," Journal of the National Cancer Institute [J. NATL. CANCER INST.], vol. 86, no. 2, pp. 99-105, 1994
9)Sun-Care Chemical Proves Toxic in Lab Tests 10/15/00
10)Sunscreens May Not Prevent Melanoma
11)Absorbing Titanium from Sunscreens
12) Serpone, N; Salinaro, A; Emeline, A, "Deleterious effects of sunscreen titanium dioxide nanoparticles on DNA. Efforts to limit DNA damage by particle surface modification," Dept. of Chemistry and Biochemistry Concordia University, Montreal, Que., H3G 1M8, Canada Nanoparticles and Nanostructured Surfaces: Novel Reporters with Biological Applications, San Jose, CA, United States, 01/24-25/01 PROC SPIE INT SOC OPT ENG. Vol. 4258, pp. 86-98. 2001.
13) de Fine Olivarius F; Wulf HC; Crosby J; Norval M; "Sunscreen protection against cis-urocanic acid production in human skin," Department of Dermatology, Bispebjerg Hospital, University of Copenhagen, Denmark. Acta dermato-venereologica, 1999 Nov, 79(6):426-30
14) Diffey BL; Grice J; "The influence of sunscreen type on photoprotection," Regional Medical Physics Department, Dryburn Hospital, Durham, U.K. The British journal of dermatology, 1997 Jul, 137(1):103-5

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