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Men, women, and children who are more than 6 months old should use sunscreen every day. This includes people who tan easily and people who don’t tan easily. Remember, whether you are sunburned or not, your skin will be damaged by the sun for the rest of your life. According to its principle, sunscreen can be divided into the following two categories.
Chemical sunscreen
This type of sunscreen relies on absorbing ultraviolet rays and then neutralizing them to release heat. Sensitive skin types may find this formula irritating to their skin. After smearing, it also takes a few minutes to work, which is about 15-20 minutes.
Physical sunscreen
This type of sunscreen relies on reflection to keep the light away from the skin. When you use physical sunscreen, you can imagine that there is a barrier or shield on your skin. This is useful for sensitive skin types because it is less irritating and most effective. It can be used immediately after smearing. However, it feels very thick and usually leaves a white cast on the skin.
Among the many high-tech products that add nanoparticles, there are two kinds of nanoparticles added to sunscreen: titanium dioxide (TiO2) and zinc oxide (ZnO) nanoparticles.
Lighter and more durable
Large particles of zinc oxide and titanium dioxide have been used in sunscreen for decades and can reflect or absorb ultraviolet rays that can cause cancer. Traditional sunscreen appears white after application because these large particles reflect visible light. When zinc oxide and titanium dioxide are made into nanoscale particles, the size is only 25-50 nanometers, and the role they play has changed.
Although zinc oxide and titanium dioxide nanoparticles are clustered together when mixed into sunscreen, they still maintain a high degree of attraction to ultraviolet rays; at the same time, they also absorb and scatter visible light, thus making the light near the skin appear transparent.
Compared with other UV filtering ingredients, they are more stable, do not need to be reapplied repeatedly, and are less likely to cause allergic and irritating reactions. Another benefit is that nano-sized zinc oxide and titanium dioxide feel “thinner” and do not give the skin a heavy, solidified feeling.
To sum up, sunscreen containing nanoparticles is the real winner in the field of sunscreen. You can apply them in large quantities to protect your skin from the hot sun.
Safer and more high-end
Nanoparticles made of metal oxides that can damage the skin after being incorporated into sunscreen are mainly those that can penetrate the skin. Available scientific evidence shows that the penetration of zinc oxide and titanium dioxide nanoparticles into the skin is negligible and these two have been approved by the FDA as an active ingredient to sunscreen. They can’t even penetrate the stratum corneum (consisted of dead cells) in the outermost layer of the skin. You know, every day, the outermost layer of people’s skin will strip off millions of dead cells.
An Australian researcher recently found that immune cells can collect and decompose zinc oxide nanoparticles. Simon James, who involved in the study, said: “Our research shows that the body’s immune system has the ability to remove nanoparticles that slip into the skin.” James is also aware that his research is still inadequate due to using cells cultured in vitro and nanoparticles that are not mixed with sunscreen. He believes that further experiments are needed to perfect the conclusion, but we can at least understand that the immune system does have the ability to degrade zinc oxide nanoparticles.
Other researchers are conducting similar experiments to examine the long-term and short-term effects of metal oxides on the human body. But they also point out that if the skin is not protected, it can be too harmful if it is exposed to the sun for too long; compared with this, other minor injuries are tolerated.
Scientists also say that even if trace amounts of zinc enter the human body, its amount is negligible compared to the existing amount of zinc in blood and tissue. So, sunscreen containing zinc oxide nanoparticles is safe. In any case, the Skin Cancer Foundation believes that the best sunscreen is the one you are most likely to use, as long as it provides safe and effective protection, and is broad spectrum with an SPF 15 or higher.
Reference:
James, S. A., Feltis, B. N., de Jonge, M. D., Sridhar, M., Kimpton, J. A., Altissimo, M., … & Paterson, D. J. (2013). Quantification of ZnO nanoparticle uptake, distribution, and dissolution within individual human macrophages. ACS nano, 7(12), 10621-10635.