Sun Protection Factor

The sun protection factor (SPF) indicates by how much the sunscreen extends the time until erythema, i.e. redness of the skin, occurs under exposure to sunlight, or in other words, how long the body’s auto-protection time is prolonged. This time naturally depends on the pigmentation type of an individual’s skin, the geographical latitude, and the time of day. People with reddish-blond hair and freckles, i.e. photobiological skin type I, often have an auto-protection time of only 5 to 10 minutes in summer. So a sunscreen with an SPF of 30 for UVB radiation can protect the skin for about 3 hours. However, people should never stay out for this maximum period and expose themselves to the sun until a sunburn reaction occurs as already well before this, i.e. after about half the time, chronic light damage and skin ageing start to occur. Renewed application of a sunscreen with the same SPF does not extend the time of protection. Nevertheless, it …

Sun Protection

The simplest form of protection against the sun is to wear clothing, including a hat. However, thin cotton fabrics only provide limited protection against sunlight. They have a sun protection factor (SPF) of 10 for UVB radiation. A wet cotton T-shirt still allows about 20 % of UV radiation to pass, so has an SPF of 5. Therefore, even when wearing clothing, it is still recommended also to apply a waterproof sunscreen. Because of this only limited level of protection provided by thin textiles, in countries with high sunlight intensity such as Australia working clothes and also children’s clothes are now being produced with higher sun protection factors. Some textiles with a high sun protection factor for children are also available in Germany. There is a wide range of sunscreen products that differ in the type of filter they use, e.g. against UVA radiation only or against UVA and UVB together (broad-band filter). But they also differ in the type …