The SPF (Sun Protection Factor) on sunscreen packaging is one of the most effective marketing tools to persuade people to buy a product. SPF is the amount of protection the skin will receive from direct, visible damage from UV radiation, also known as sunburn, known as erythema. Redness, the first visible sign of skin damage, is caused by UV light in the 290-400 nm wavelength range.
SPF alone cannot protect the skin from UVB radiation, as some UVA radiation in the 320-400 nm wavelength range also has the potential to cause sunburn. In fact, approximately 15% of all radiation that causes erythema (sunburn) is in this range. So, both UVA and UVB have their own risks.
Knowing the sun protection factor is important for consumers, as with the SPF and the natural protection time, it is possible to calculate the theoretical maximum time that can be spent in the sun: by multiplying your natural protection time by the sun protection factor.
The natural protection time is the time that you can stay in the sun without protection until the first signs of sunburn are observed. This value varies greatly depending on the skin type.
According to the Fitzpatrick scale, there are six skin types for sun protection:
- Type I – very fair skin, burns in less than 10 minutes and never tans.
- Type II – fair skin, burns in a maximum of 20 minutes and tans very little.
- Type III – medium skin, burns occasionally in about 30 minutes and tans gradually.
- Type IV – olive skin, burns rarely and tans easily in 40 minutes.
- Type V – Dark skin, rarely burns and tans well for up to 60 minutes.
- Type VI – Very dark skin, almost never burns and can tolerate more than an hour easily.
If you have type 2 skin, you will see the first signs of redness after about 10 minutes and using a sunscreen with SPF 20 at best, you can theoretically stay in the sun for 200 minutes. In reality, the duration will often be shorter due to infrequent use of the product, fading after swimming, etc.
It seems that most consumers do not get the maximum benefit of SPF protection from their sunscreen because they do not apply enough product to their skin. Research shows that there is a direct relationship between the amount applied and the sun protection factor. Assuming about half the recommended amount is used, this results in an actual sun protection factor of about 50% of the declared amount.
SPF is measured using a dose of 2 mg/cm2 applied to the body. These values are not used in real life. The “normal” dose is only about 1 mg/cm2. This means that the actual SPF (due to the dose) is only about half of the claimed SPF.
However, SPF can only be considered as an indicator of the level of protection. Sun protection products should not only provide protection against sunburn by having effective UVB, UVA and/or broad-band filters, but they should also significantly reduce the risk of skin cancer and prevent UV-related aging. To achieve all of this, the sunscreen product must have a) high protective performance across the entire light spectrum and b) a good and sensible combination of UV filters, oils and other ingredients in the formulation.
In other words, a good sunscreen is more than just a high SPF.
