In 1978, the FDA recognized SPF as the standard for measuring sun protection.
SPF (Sun protection factor) is a number that represents the ratio between the dose of UV radiation (predominantly UVB radiation), which leads to the appearance of erythema in protected skin, and the dose that leads to the appearance of erythema in unprotected skin, i.e.:
SPF = MED (minimum erythemal dose) of protected skin (J/cm2)/MED of unprotected skin (J/cm2).
Therefore, a preparation with SPF 2 can absorb 50% of the incoming radiation. If the product has SPF 15, it can absorb approximately 93%, and SPF 30 97%, while SPF 50 absorbs about 98% of solar radiation, i.e. UVB rays. Higher protection factors have a greater effect, but it is not linear. To help users understand SPF values correctly, the FDA has divided sunscreens into three categories according to the degree of protection:

  • Minimum protection SPF 2 to 11
  • Moderate protection SPF 12 to 29
  • High protection SPF 30 and higher

The fact that the FDA has classified this product category as OTC drugs since 1978 shows how important sun protection preparations are. Over-the-counter drugs, and not as cosmetic products, as is traditionally the case in the Europe.

UV-induced erythema (redness) as mentioned is mainly attributed to UVB radiation, but UVA radiation also contributes to it. However, the concept of SPF, which primarily shows protection against UVB rays, i.e., UVB-induced erythema has persisted for many decades as the sole measure of sun protection, despite advances in the study of UV radiation, suggesting that UVA may play a significant role in photoaging.

There is indisputable evidence that daily photoprotection and the use of sunscreen play an important role in the prevention of photoaging.

Not only have sunscreens been shown to prevent photoaging, but evidence also suggests that they may play a role in slowing down processes caused by extrinsic aging, such as smoking, poor diet, air pollution, lack of sleep, and frequent facial expressions. In one prospective study, 32 subjects were asked to apply a photostable broad-spectrum sunscreen (SPF 30) daily for 52 weeks. At the end of the study, significant improvements in skin texture, skin appearance and pigmentation uniformity were observed, with 100% of subjects showing improvement in skin texture.


A successfully formulated preparation for sun protection is a multi-functional product that, above all, should provide adequate protection from the sun, but also additionally hydrate the skin and protect it from oxidative stress, i.e., to have a comprehensive "anti-aging" effect. This is achieved by incorporating permitted, effective UV organic and inorganic filters in sufficient, recommended concentrations.

UV filters must meet a number of requirements, since the preparations they contain are used in unfavorable conditions - under the influence of the sun, they are applied to large areas of the skin, which is often damaged by the action of the sun, salt, sand and the like.

Requirements for modern UV filters are:

  • to be effective in absorbing UVA and/or UVB rays
  • chemically stable
  • non-volatile
  • resistant to perspiration
  • do not stain the skin
  • not to penetrate the skin and possibly be absorbed into the systemic circulation
  • to be tasteless and odorless
  • to be toxicologically acceptable
  • to be tolerable for the skin and mucous membranes (they do not cause irritation, sensitization, phototoxicity and photoallergic reactions)
  • must not be teratogenic or mutagenic.