The only prerequisite before buying a cream for treating keratosis is visiting a dermatologist for observation and provision of a prescription. Afterwards, there are many drug stores where the cream can be purchased. The cost of creams used in keratosis treatment is also relatively affordable compared with other methods of treating the conditions. Topical creams have been proven to be very good in treating senile keratosis. Compared to other methods of treating keratosis, creams have very little risk of causing scarring on the affected areas.
Sun Protection Factors (SPF) are a useful guide to the efficacy of a sunscreen. In New Zealand most manufacturers adhere to the requirements of a voluntary Australian and New Zealand Standard in which the labelled SPF can be up to 50+ (AS/NZS 2604:2012). The SPF is calculated from in-vivo testing, and is the ratio of the time for the skin to burn when exposed to solar simulating UVR with the sunscreen at a thickness of 2mg/cm 2 , compared without the sunscreen. Thus white skin that normally burns in 10 minutes will burn in 150 minutes (2 ½ hours) with SPF 15 sunscreen, however often it is reapplied. In general, sunscreens are much less effective than predicted by their SPF number as they are applied significantly less thickly than is tested and are rubbed, sweated or washed off.