Sunscreen Use

Controversies, Challenges and Regulatory Aspects

M. Lodén, H. Beitner; H. Gonzalez; D.W. Edström; U. Åkerström; J. Austad; I. Buraczewska-Norin; M. Matsson; H.C. Wulf

Disclosures

The British Journal of Dermatology. 2011;165(2):255–262 

In This Article

Do Sunscreen Products Cause Damage to Human Health?

The safety of many chemical substances has been questioned during recent decades. UV filters in sunscreen products have been challenged on the basis that, for example, they may:

  1. Be toxic:

    • Penetrate the skin resulting in systemic exposure with unknown consequences;[8,9]

    • Be endocrine disruptors;[10–12]

    • Cause contact and photocontact allergies.[13–19]

  2. Increase the risk of melanoma.[20]

  3. Prevent vitamin D formation.[5]

Toxicity

Formulations with UV filters may penetrate the skin and reach the circulatory system.[8–10] The penetration of dissolved organic sunscreen filters is usually between 0·1% and 5%,[8] and is not influenced by UVR.[9] UV filters in the form of insoluble particles (e.g. titanium dioxide and methylene bis-benzotriazolyl tetramethylbutylphenol) do not penetrate into or through human skin, which suggests that they pose no potential risk of systemic toxicity.[21,22]

The margin of safety (MoS) for systemic exposure to a given UV filter is estimated by comparing the potential human exposure with the 'no adverse effect level' (NOAEL) determined in subchronic or chronic toxicity studies in animals. Only substances with a MoS of at least 100-fold and a safe toxicological profile are approved for human use. As an example, the determination of the MoS for the UV filter homosalate, made by the EU Scientific Committee on Consumer Products, was determined to be 167 (i.e. > 100) based on the daily use of sunscreens (18·0 g), the maximum dermal absorption of the UV filter (2%) and the maximum allowed content of homosalate (10%) (Table 1).[23] The actual MoS is probably higher, as the concentrations used are often not the maximum allowed and the duration of exposure of sunscreens is limited (NOAEL determined on long-term daily feeding of the animals) are usually lower.

However, the risk assessments for older substances have been questioned, especially regarding safety level for endocrine disruption, where selected UV filters have been found to be endocrine disruptors in animals. However, there are no indications of endocrine disruption by UV filters in humans, either of sexual hormones or of the thyroid hormones.[10,11] A critical review of the literature has also been unable to link UV filter exposure to endocrine-disruptive effects in humans.[24]

In addition to potential systemic toxicity, topically applied products may cause adverse skin reactions. With the increasing use of sunscreens and exposure to UV filters in daily-use face creams, soluble UV filters have become more frequent photoallergens and contact allergens (Table 2).[13–16,25–27] The frequency is rare and appears to be equally distributed between photoallergy and contact allergy.[15]

The use of UV filters is regulated by the responsible authorities and the filters appear on an approved or a positive list in many countries. Prior to their approval and placement on a positive list in the EU, the United States and Japan, UV filters have to pass a stringent toxicological safety evaluation. This includes studies on acute toxicity, subchronic and chronic toxicity, reproductive toxicity, genotoxicity, photogenotoxicity, carcinogenicity, irritation, sensitization, phototoxicity and photosensitization. In the U.S. photocarcinogenicity is also addressed. Such approvals do not substitute for individual product safety, but provide some assurance that the included UV filters provide a general support of human safety that balances the risks induced by UVR.

Melanoma

Sunscreen users have also been asserted to be at increased risk of melanoma.[20] However, the suggested association between melanoma and sunscreen use has been explained by failure to control for confounding factors, such as the sun exposure dose.[28] It was also recently reported that regular use of sunscreen in Australia appeared to actually reduce the incidence of new primary melanomas and also protect from invasive melanoma[29] The use of sunscreens has also been found to delay the formation of naevi in light-skinned children.[30] The number of naevi is an indicator of melanoma risk.[31] However, it may take decades to confirm a protective association between melanoma and the use of modern sunscreens to prevent skin cancer.[28]

Actinic Keratosis and Squamous Cell Carcinoma

Sunscreens are able to prevent formation of actinic keratosis and squamous cell carcinoma.[32,33] Regular use of broad-spectrum sunscreens, as part of a consistent UV-protection strategy, has been shown to prevent the development of further actinic keratosis and invasive squamous cell carcinoma in immune-compromised organ transplant recipients.[34]

Vitamin D

Photoprotection by sunscreens has been criticized not only for providing insufficient protection of the skin, but also for preventing synthesis of vitamin D.[5,6] It has thus been suggested that photoprotection adversely affects vitamin D status and consequently increases the incidence of and worsens the prognosis for some internal cancers.[6,7] Increased exposure to sunlight has been proposed for risk groups in Australia to prevent vitamin D deficiency.[35] However, the general relation between vitamin D and cancer is not well documented.[36] Marks et al.[37] have also shown that subjects who regularly apply sunscreens during the summer in Australia end up with the same vitamin D level as a control group without sunscreen use, suggesting that sunscreen use does not increase the risks for internal cancers but instead protects against skin lesions. The advocated way to increase the level of vitamin D is by the oral route.[38,39]

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