Sunscreens made from ground wood reach SPF over 180

Sunscreens enriched with lignin, a component of wood, can have sun protection factors (SPF) that exceed 180. They also appear to last longer and penetrate less into the skin than existing products, potentially making them safer.

Sunscreens are an important defense against skin cancer, but in recent years there has been growing discomfort and confusion about their safety. A recent US overview found that 14 percent of young adults think that daily use of sunscreen is more harmful than direct sun exposure.

This comes after the US Food and Drug Administration (FDA) released research showing that several common ingredients in sunscreens can enter the bloodstream through the skin. This does not necessarily mean that they are harmful and long-term studies found no risks associated with daily sunscreen use, but the FDA called for more research to investigate.

In the meantime, scientists are looking for natural alternatives to existing sunscreen chemicals that may be safer for human health while being less harmful to corals and other marine life when they wash up in the oceans.

One of nature’s most promising sun protection substances is lignin, which glues plant cell walls together and gives tree trunks strength. It also protects plants from ultraviolet (UV) radiation from the sun.

The main challenge for the use of lignin was its extraction from wood. Traditional methods use harsh chemicals that turn the lignin from a light color to almost black, making it unsuitable for use in sunscreens.

Now two groups at the South China University of Technology have found ways to extract lignin from wood without darkening it, and then use it to make sunscreen.

One group led by Jun Liextracted pale yellow lignin from poplar wood by grinding and sieving into a fine powder. The lignin was then released from the powder using ultrasonic waves. The second group led by Yong Qianextracted pale pink lignin from birch wood using a similarly mild procedure.

The two groups then processed the lignin to turn it into nanoparticles, which they mixed with ordinary white creams to make sunscreens.

Subsequent testing showed that the light yellow lignin sunscreen had an SPF of 20, while the light pink had an SPF of 19, so both were moderately effective. They were also broad-spectrum, meaning they protected against two types of skin-damaging UV rays, UVA and UVB. When spread on the skin, they blended with fair skin tones and felt pleasantly smooth.

Since these lignin sunscreens are not as protective as many sunscreens on the market that have SPF values ​​of 50+, Qian and his colleagues tried combining them with existing ingredients. When the team encapsulated two common sunscreen ingredients, avobenzone and octinoxate, in lignin nanoparticles, their SPF jumped to more than 180. However, it should be noted that sunscreens cannot be marketed as more than SPF 50+ because SPF values ​​higher than 50 do not provide much more protection as the scale works.

Placing existing sunscreens in lignin nanoparticles also made them more resistant to breakdown, allowing them to last longer in the sun. It also prevented them from penetrating the skin, potentially making them safer.

Qian says he and his colleagues are now further testing one of their lignin nanoparticle sunscreens on humans. For now, “it’s safe and has a good sunscreen,” she says.

In addition to lignin, other natural sunscreens being investigated include components of seaweed, ferns, squid and human hair.

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