Does shea butter protect against the sun?

The sun is essential for skin health. Among other things, it stimulates the synthesis of vitamin D, which plays a role in the quality of bone and muscle tissue. However, the sun is a source of heat and this is not always beneficial for the skin.

UV rays are electromagnetic radiations originating from the sun. They are not perceptible to the naked eye due to their short wavelength. UV rays accelerate dehydration and can disrupt the skin's balance, which can weaken the skin's barrier function. This can result in an increase in the transepidermal water loss and therefore a too low skin hydration rate. There are three types of UV rays: UVA, UVB and UVC.

• The UVA rays penetrate the epidermis and destroy collagen and elastin fibres. They trigger the formation of free radicals which reduce the skin's natural repair capacity and promote premature skin ageing. They are responsible for pigmentation spots and the appearance of wrinkles.

• UVB rays have a low penetration into the dermis. They induce the production of melanin by melanocytes and the thickening of the epidermis. They are responsible for sunburn and the majority of skin cancers, as they directly interact with DNA cells.

• The UVC rays are the most harmful UV rays, but they are completely filtered by the ozone layer and do not reach the Earth's surface.

Shea butter is said to provide basic protection when exposed to the sun, considered equivalent to a low-level UV filter. But what is the reality?

The triterpenic alcohol cinnamate esters, the main component of the unsaponifiable fraction of shea butter, have a strong absorption of UV rays between 250 and 300 nm. When added to a sun protection product, they synergistically enhance the absorption of UVB rays with the sunscreen filters.

However, studies have shown that this triterpene fraction only provides a low sun protection factor: a SPF of 4. Therefore, it is important to note that shea butter alone does not constitute effective sun protection. It can be used in conjunction with a photoprotective care product and act as a SPF boosting compound to enhance the effectiveness of UV filters.

Shea butter is not officially recognised and listed as a sun filter and does not appear in Annex VI of the cosmetic regulation among the other authorised UV filters. However, it remains useful to provide additional support in sun care products with authorised ultraviolet filters.

How to use it?

For shea butter to be effective, it simply needs to be applied in its pure form to the entire skin before the sunscreen. It will leave a slight film on the skin to protect and shield it from the sun. It can also already be incorporated into sunscreens to enhance the effectiveness of the SPF in vivo (synergy with UV filters) and help to protect the chemical integrity of organic UV filters.

Our skin is naturally equipped to defend against UV radiation thanks to the melanin. However, when the skin is overly exposed to the sun, melanin no longer effectively filters UV rays, leading to the onset of sunburn: this is the phenomenon of oxidative stress. In brief, certain molecules lose one or more electrons and transform into free radicals. Unstable, these reactive molecules can cause damage to cells and constituents.

Indeed, the vitamin E or tocopherol, found in shea butter, protects against external aggressions such as UV radiation and chemical pollution. It has the ability to donate an electron to a free radical without becoming unstable. The free radical is then stabilised, less reactive and the oxidation cascade of molecules is halted.

• BIRD K. Moisturising power of Shea butter highlighted by scientific studies. Cosmetics Formulation & Science (2009).

• BABY A. R. &al. Butyrospermum parkii butter increased the photostability and in vivo SPF of a molded sunscreen system. Journal of Cosmetic Dermatology (2020).