Topically applied sunscreens protect by absorbing or reflecting radiation at the skin surface. UV filters can be grouped into two broad categories: organic (previously called chemical) and inorganic (previously called physical) (Yaar and Gilchrest, 2007). Organic sunscreens absorb UVR, convert it into heat, and thus prevent photons from interacting with molecules in the skin. Organic sunscreens are usually „invisible‟ and hence cosmetically appealing.
Sun Protection Factor (SPF) of a sunscreen is primarily a measure of protection against UVB. It is defined as the minimal perceptible erythema, or minimal erythema dose (MED) ratio between sunscreen-protected and unprotected skin. If a person normally experiences the onset of redness to unprotected skin after 10 minutes of sun exposure, sunscreen with SPF 8 would provide protection against perceptible sunburn for 80 minutes. SPFs are now also categorised as providing low to very high protection: Low protection SPF 6 to 14/Medium protection SPF 15 to 29/High protection SPF 30 to 50/Very high protection SPF 50 + (i.e. SPF 50+).
It is recommended that people select sunscreens with SPF 30 or higher (Palm and O‟Donoghue, 2007) because they generally do not apply sufficient quantities of the product. The recommended SPF 30 takes into account these behavioural factors that lead to a reduced level of protection (if applied adequately, then SPF 15 is sufficient).
Sunscreens that offer both UVA and UVB protection are called „broad spectrum‟. The ‘star system’ indicates a product’s UVA protection, i.e.the % of UVA radiation absorbed by the sunscreen in comparison to UVB or the ratio between the level of protection afforded by the UVB protection and the UVA protection. Five stars indicates excellent protection against UVA equal to the SPF against burning, whereas one or more stars implies UVA protection equal to one or more fifths of the SPF against burning (Wahie et al., 2007). If choosing a low SPF, it may have a high level of stars, not because it is providing high UVA protection, but because the ratio between the UVA and UVB protection is about the same. That is why it is important to use a high SPF in conjunction with high UVA protection!
The Sunscreen Rules
- The overall message in terms of sunscreen use is – more is better.
- Choose a sunscreen labelled „photostable, broad spectrum‟ which offers both UVA and UVB protection.
- Use a „high protection‟ sunscreen of at least SPF 30 to protect against UVB and high UVA protection - at least 4 stars and the circular UVA logo.
- Apply half an hour before going out in the sun, and half an hour after commencing sun exposure to prevent an additional 65 to 80 percent of UV light (Lowe, 1990) and corrects missed patches of skin. Don’t forget your the other exposed areas – head, neck and ears (Fry and Verne, 2003).
- Reapply sunscreen at least every two hours, and immediately after contact with water, even if the sunscreen is „water resistant‟, and also after towel drying.
- Apply sunscreen liberally. Adults should apply an equivalent to a full shot glass (~35 ml) evenly on the whole body (Wulf et al., 1997) and rub it in after application in order to avoid skip areas (Neale et al. 2002, Barr 2005).
- Aftercare is also important. Apply aftersun products to moisturise your skin after sun exposure.
Preventing skin cancer
The role of photoprotection products against malignant melanoma is complex. A systematic review in 2003 failed to show that sunscreen use had any preventive effect (Dennis et al., 2003). However, used appropriately, sunscreens have been shown to be extremely efficient against burning, DNA damage and immunosuppression of the skin. Regular and careful use of sunscreens has been clearly shown to reduce the incidence of actinic keratoses and squamous cell carcinomas but not necessarily basal cell carcinomas (Darlington et al., 2003; Green et al., 1999).