Sunburn, Sunscreen, Sunblock, and Zinc Oxide

Back in 1995, I asked on the Internet for peoples' experience with, and advice upon, the use of items for protecting marathon swimmers from sunburn on swims lasting for as long as 36 hours. The main advice involved the use of traditional suncreens and sunblocks - with the suggestion that application for several days BEFORE the swim would improve their effectiveness.

Since that time, members of SSO have experimented and concluded that Zinc Oxide creams were by far the most effective protection and longest lasting of the materials they could find. These creams have been used for many years to protect the skin of babies from the effects of faeces, urine etc. but are not cheap when purchased in the small jars or tubes used for the care of infants' skin.

Dr Mel Siff's collection of the following scientific articles on this topic is, therefore, of great value. It concludes the value of Zinc Oxide creams as the most effective solution, not only to the prevention of the skin reddening caused by sunburn, but also in the prevention of the longer-term risk of skin cancer resulting from ultraviolet damage to the skin. The most notable paper, in respect to Zinc Oxide creams, by Mitchnick, Fairhurst & Pinnell (1999) is highlighted in red.

Most of these articles can be accessed through the National Institute of Health web site that provides free access to Medline literature searches. Links to the NIH site are provided on each reference, but the reader may wish to use the NIH site for more comprehensive searches.

Posted on SportScience by Dr Mel C Siff on their E-mail List, item #725, 3rd October 1999:

Many cricketers, surfers, yachtsfolk, mountaineers, tennis players, triathletes, beach voleyballers, cross country skiers and other athletes who are exposed to prolonged solar exposure rely on sunscreens to protect themselves from skin cancer, but their efficacy and safety are now being brought into further doubt by recent research.

It has been suggested that only thick layers of cream make a significant difference and that the reflectivity of the cream also plays a definite role. Perspiration and sports activities in the water often compromise the adequacy of protective cream, so athletes may be labouring under the misconception that these creams are as effective as is implied by the protection factor quoted on the products.

Furthermore, the news article refers to research speculating that suncreens may even increase the risk of skin cancer. How many of the advertisements are to be believed and which laboratory reports are we to accept now?

Posted on SportScience by Dr Mel C Siff on their E-mail List, item #726, 5th October 1999:

Someone suggested that the 1994 reference that I supplied earlier on this topic was 'dated' or insufficient to question the value of sunscreen protection to sun-exposed athletes. Just to dispel this notion, here is some even more recent information - outdoor athletes should pay special attention to the reference to Mitchnick, Fairhurst & Pinnell (1999).

Azurdia RM et al. (1999): Sunscreen application by photosensitive patients is inadequate for protection. Br J Dermatol 1999;140(2):255-258

Photosensitive patients fail to apply sunscreen in some prominently exposed sites, and use average thicknesses far less than the manufacturers' recommendation (2 mg/cm2). The level of protection is much lower than anticipated from the stated SPF of the product.

Damian D, Halliday G & Barnetson R (1997): Broad-spectrum sunscreens provide greater protection against ultraviolet-radiation-induced suppression of contact hypersensitivity to a recall antigen in humans. J Invest Dermatol 1997;109(2):146-51

Immune protection is provided only by sunscreens filtering both UVA and UVB.

Green A, Williams G, et al (1999): Daily sunscreen application and betacarotene supplementation in prevention of basal-cell and squamous-cell carcinomas of the skin: a randomised controlled trial. Lancet 1999;354(9180):723-9

Nearly 1400 participants underwent full skin examination by a dermatologist in the follow-up period. Of these, 250 developed 758 new skin cancers during the follow-up period. There were no significant differences in the incidence of first new skin cancers between groups randomly assigned daily sunscreen and no daily sunscreen (basal-cell carcinoma and squamous-cell carcinoma).

Gulston M & Knowland J (1999): Illumination of human keratinocytes in the presence of the sunscreen ingredient Padimate-O and through an SPF-15 sunscreen reduces direct photodamage to DNA but increases strand breaks. Mutat Res 1999 Jul 21;444(1):49-60

If the sunscreen is not in contact with keratinocytes it reduces direct DNA damage from sunlight (ESS). However, any Padimate-O in contact with the cells substantially increases indirect damage (strand breaks) by an estimated 75 times even though the film of sunscreen reduces direct photodamage.

Heenen M (1999): Photoprotection, cancer protection and solar protection factor [in French]. Rev Med Brux 1999 Jun;20(3):143-6

Sun protection factor of sunscreens is assessed by their ability to inhibit UV-induced erythema. A correlation between sun sensitivity and density of DNA damage has been established. However, the ability of suberythematous irradiation to induce DNA damage suggests that this correlation is not linear. Therefore, exposure to sunrays, extended because of a delayed erythema, can lead to more DNA damage than it is usually believed. The danger of long term of sunscreens use is therefore real, more especially as they may offer different protection factors for different biological end-points.

Journe F et al. (1999): Sunscreen sensitization: a 5-year study. Acta Derm Venereol 1999;79(3):211-3

The purpose of this study was to evaluate the prevalence of sunscreen contact allergy and/or contact photoallergy in 370 patients with suspected photodermatitis. Patch and photopatch tests were performed using the French Society of Photodermatology (SFPD) standard series. A total of 57 cases of contact allergy and/or photocontact allergy to sunscreens were diagnosed (15.4%). Amongst these, 27 reactions were related to oxybenzone and 14 to isopropyl dibenzoylmethane.

Mackie BS & Mackie LE (1999): The PABA story. Australas J Dermatol 1999 Feb;40(1):51-3

The qualities of para-aminobenzoic acid (PABA) are discussed and an account is given of how it came to be the favourite sunscreen of the post World War II era. Slowly, however, dermatologists became aware that it was a fairly common sensitizer and that it tended to cross-sensitize with compounds of similar chemical structure both in contact with the skin and given as systemic drugs. Furthermore, continued exposure to chemicals of this type could lead to autoimmune responses especially systemic lupus erythematosus and dermatomyositis. Discussion of these complications from the use of PABA took place at two meetings of the Dermatological Association of Australia in 1964 and 1965, and played a part in the slow withdrawal of PABA from sunscreens.


Now for some better news - here is a cheap old wives cream that many of us used to protect and heal the skin and that of animals exposed to the sun several decades ago - very finely powdered zinc oxide. Our chemist used to mix at a cost of a few pennies in a suitable cream. This research article suggests that a return to this old remedy in a suitable emollient would probably be better than most of the modern sunscreens.

Mitchnick MA, Fairhurst D & Pinnell S (1999): Microfine zinc oxide (Z-cote) as a photostable UVA/UVB sunblock agent. J Am Acad Dermatol 1999 Jan;40(1):85-90

The purpose of the research was to assess the suitability of microfine zinc oxide as a broad-spectrum photoprotective agent by examining those properties generally considered important in sunscreens: attenuation spectrum, sun protection factor (SPF) contribution, photostability, and photoreactivity. It was found that microfine zinc oxide is an effective and safe sunblock that provides broad-spectrum UV protection, including protection from long-wavelength UVA.

Rosenstein BS, Weinstock M & Habib R (1999): Transmittance spectra and theoretical sun protection factors for a series of sunscreen-containing sun care products. Photodermatol Photoimmunol Photomed 1999;15(2):75-80

Sun care products containing sunscreens are widely used, but consumers are generally unaware of the important differences in the ability of these lotions to block exposure to the ultraviolet A (UVA) portion of the solar spectrum.

The UVA transmitted through the sunscreens that claimed UVA protection on the bottle label varied from as little as 6% to as much as 52%. In addition, it was determined from the CIE (Scientific standards tests) effectiveness spectra that any erythema induced following application of the tested lotions would be caused by the UVA portion of the solar spectrum for all, but one, of the products examined. This tudy emphasizes the necessity for better guidance to the consumer as to the ability of sun care products to provide protection against UVA exposure.

Tarras-Wahlberg N et al. (1999): Changes in Ultraviolet Absorption of Sunscreens After Ultraviolet Irradiation. J Invest Dermatol 1999 Oct;113(4):547-553

This study including gas chromatography and mass spectrometry analysis indicated that some of the photoactive organic species commonly used today in sunscreens are unstable following ultraviolet irradiation.

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Created: 17th October 1999
Last Updated: 23rd March 2003