Can sunscreen be applied or not?

Recently, a medical news broke out: JAMA published a research result: after several volunteers used sunscreen, the concentration, peak concentration, half-life and residual concentration on the seventh day all exceeded the standard, and the peak concentration exceeded the threshold concentration stipulated by the Food and Drug Administration (FDA). Under this news, everyone commented that the sunscreen that should have played a protective role has also become unsafe. It is poisonous, sunburned by the sun and may cause skin cancer. How to choose? Don't be afraid! Next, I will take you step by step into the truth! Interpret the data rationally and don't panic too much. This study is actually a study sponsored and carried out by the FDA itself, aiming to study whether four commonly used sunscreen ingredients can enter the blood circulation through the skin. The four commonly used sunscreen ingredients tested are: levoavobenzone, levohydroxyphenyl ketone, levooctyl propylene, and levoicariin. A total of 24 volunteers participated in the study, and each volunteer was required to apply 2mg sunscreen on every square centimeter of skin, covering 75% of the whole body. What is this concept? The general sunscreen is 30g, 50g and 60g, and the most famous one is 60g, which means that each volunteer has to apply nearly 2 bottles of sunscreen every day. The results showed that the highest blood concentrations of four sunscreen components in volunteers exceeded the threshold concentration of 0.5ng/mL (nanogram per milliliter) originally recommended by FDA. At the same time, in the following days, the blood concentrations of these components gradually increased. Does that sound scary? In fact, sunscreen ingredients can be absorbed into the blood, and it is common for the cumulative concentration to increase with the extension of use time. Not only sunscreen ingredients, but also any skin care products and external drugs that act on the skin surface can be absorbed into the blood, which is called "transdermal absorption" in pharmacy. Skin is a kind of mucous membrane, and capillaries are all over the skin. Skin care products and topical drugs applied to the skin can be absorbed by epidermis and dermis, enter capillaries, and then enter the blood circulation of the whole body. But the skin has a certain barrier effect. Compared with direct entry into blood vessels (intravenous route) and oral administration, the amount of these substances passing through the skin and finally entering the blood is not much. Foreign chemicals will be excreted by liver and kidney metabolism after entering the human body. This process will take some time. Generally, the half-life is used to evaluate the metabolism and excretion rate of chemicals. If chemicals enter the human body faster than they are discharged, the concentration of chemicals in the human body will be higher and higher. This is also the reason why we do not advocate the use of irregular skin care products and topical drugs, because the heavy metals or other toxic substances that may be contained in these drugs will enter the human body and accumulate over time, eventually producing toxicity. At present, there is no clear conclusion whether the four components mentioned in this study will endanger health if they enter the human body in excess of the domain dose. This is also the next step for the FDA to evaluate. The study also mentioned that the harm of high concentration sunscreen is not clear at present. Research only proves that sunscreen enters the human body more than expected. Since everyone knows that sunscreen ingredients can enter the human body, why does the FDA conduct this research? The key point is that this threshold concentration is 0.5ng/mL. This concentration means that below this dose, the cancer risk of any unknown chemical is less than one in 100,000. In other words, this study shows that if sunscreen is used at the maximum dose, it may not be as safe as expected, and the cancer risk cannot be reduced below one in 100,000. Does this mean that the risk of cancer will increase? The FDA is intriguing to say that they don't know because toxicology research has not been carried out yet. For the entire sunscreen industry, this research is undoubtedly a thunder. The study was conducted by FDA personally, and the results proved that it was not as safe as expected. Then the next step is to require enterprises to strengthen the safety assessment of their sunscreen toxicology, and may further tighten regulatory policies. What's the impact on those of us who usually use sunscreen? Nothing more than the following two points: 1. Generally speaking, we don't need such a high dose of sunscreen, so it may be safe for us to use sunscreen every day (that is, the highest concentration in our body is less than 0.5 ng/ml); 2. It is suggested that skin care products for external use can be absorbed by the human body. When using them, you should choose regular and approved skin care products, and don't use three-no products. Sunscreen and the sun, should we go left or right? It is inevitable that some friends are worried about sun protection and feel unsafe. So is it a healthy choice to directly expose your skin to the sun without sunscreen? Obviously not. For so many years, so many beauty and skin care bloggers have painstakingly educated everyone to wear sunscreen when going out, not only to promote products, but also to remind everyone of the impact of ultraviolet rays on health. Sunlight doesn't just tan you. Ultraviolet rays can also destroy free radicals, accelerate aging, and cause wrinkles and spots. Some days or places with strong sunshine may also burn the skin, causing skin lesions and molting. Even more frightening, it is also the most important factor that causes skin cancer. So sun protection is very necessary. How to prevent sun more effectively and scientifically? First of all, there is no need to over-interpret the toxicity of sunscreen because of this research. You should wear sunscreen or you should wear sunscreen. Secondly, sunscreen can be mainly divided into physical sunscreen and chemical sunscreen. Zinc oxide and titanium dioxide are the most common physical sunscreen components, and physical sunscreen generally reflects ultraviolet rays; The four ingredients mentioned above that enter human blood: Avobenzone, Hydroxybenzone, O 'Sullivan and Eternity are common chemical sunscreen ingredients, which can absorb the energy of ultraviolet rays and produce chemical reactions. These ingredients are not suitable for people with sensitive skin. Some special people (such as children and pregnant women) should choose sunscreen with physical sunscreen ingredients. Children are in the stage of physical development, so try to avoid using sunscreen with too many chemical components, and should use sunscreen mainly with physical sunscreen components. Pregnant women and lactating women should especially avoid using sunscreen containing oxybenzone, because oxybenzone can be detected in amniotic fluid of pregnant women and breast milk of lactating women in other studies. Thirdly, other physical sun protection measures should be used: sun umbrella, sun protection clothing, sun protection hat, sunglasses, etc. When purchasing these physical sunscreen products, you need to look for national standards and must meet the inspection standards to have a sunscreen effect. Finally, no matter what kind of sun protection measures are taken, we should try to buy recorded products in formal channels, and we must refuse some products imported from WeChat merchants and actually processed by private workshops. In the final analysis, the use of sunscreen, like the use of drugs, pays attention to the balance between risks and benefits. At present, although the absorption of sunscreen has exceeded expectations and its safety has been challenged, compared with the consequences of sunburn, accelerated aging and even skin cancer, sunscreen should still be used. In addition, if you like bronzed skin, you need to darken it, expose your skin in the sun or under beauty equipment, and apply corresponding sunscreen. I hope this research of FDA can better promote the healthy development of skin care industry, make people pay attention to the transdermal absorption of skin care ingredients, pay more attention to the safety of products, and finally benefit our consumers. Author: Li, Ph.D. in Clinical Pharmacy, Fudan University Reviewer: Wang Diya, Lecturer, Department of Military Preventive Medicine, Air Force Military Medical University Editor: The article was published by Tencent Popular Science "Popular Science Headline Creation and Promotion Project in China". Please indicate that you are from China.