This article is reproduced with permission from “Good Living Office”
Have you ever done this:
Afraid of getting sunburned on the commute, I must dig a large pile of sunscreen every day, and carefully “paste” the exposed cheeks, neck, and calves with sunscreen. But after get off work, you are exhausted, and after washing your face with water in a hurry, you are too lazy to move.
On the one hand, it is troublesome, and on the other hand, I worry that the sunscreen will rot if the sunscreen is not removed properly. The question that has plagued countless girls for several summers: Does sunscreen need special makeup removal? Is it really dangerous to not remove sunscreen for a long time?
Should I remove sunscreen
You may have heard a conclusion from many bloggers – “sunscreen must be removed”, and double cleansing, cleansing oil / cleansing water + facial cleanser, carefully clean the face every corner.
This conclusion is not empirical and does have some basis.
In 2018, researchers from West China Hospital conducted a study on sunscreens , comparing the cleansing power of water, soap-based facial cleansers, and makeup removers on sunscreens.
They conducted experiments and UV photography on 20 volunteers and showed that:
For non-waterproof sunscreens, water has some cleaning power, but only about half of the sunscreen is removed, leaving 54% of the residue. The cleansing power of facial cleanser and cleansing oil is obviously better than that of water, and both can remove more than 80% of sunscreen.
Under the UV camera, it can be seen that the face that has been removed with soap-based facial cleanser and cleansing oil is almost the same as a “clean” face.
From left to right: face covered with sunscreen (non-waterproof), face washed with water, face washed with facial cleanser, face washed with makeup remover, face without makeup Face exposed to any sunscreen / Chen, W., He, M., Xie, L., & Li, L. (2020). The optimal cleansing method for the removal of sunscreen: Water, cleanser or cleansing oil?. Journal of Cosmetic dermatology, 19(1), 180–184.
But for waterproof sunscreen, the residual rates of water, facial cleanser, and cleansing oil were 59.3%, 36.8%, and 5.8%, respectively. The cleaning power between the three was obviously pulled apart.
Under the UV camera, it can be clearly seen that water is completely useless, and only cleansing oil can basically remove it.
From left to right: face covered with sunscreen (waterproof), face washed with water, face washed with facial cleanser, face with makeup remover, never done Any face with sunscreen / Chen, W., He, M., Xie, L., & Li, L. (2020). The optimal cleansing method for the removal of sunscreen: Water, cleanser or cleansing oil?. Journal of cosmetic dermatology, 19(1), 180–184.
Simply from this experiment, one can draw the following conclusion:
For sunscreens that are not waterproof, a facial cleanser is enough. Waterproof sunscreen, must use makeup remover, makeup remover.
Theoretically yes. But there is a bug in this experiment: the environment of the experimental design is very different from our real usage scenarios in daily life .
On the beach, a woman applies sunscreen to her legs / Visual China
The above experiment was conducted in a cool and pleasant air-conditioned room with a temperature between 20-24 degrees Celsius and a humidity of 50%-60%, and the subjects applied sunscreen 30 minutes later ——That is, as soon as the sunscreen has formed a film, it is required to perform facial cleansing.
Consider the real situation of sunscreen used by migrant workers: after applying it, go out for a busy day, and only go home at night to wash your face – very likely, in the 8-9 hours of tossing, It is oily and sweating again, and a thin layer of sunscreen has been tossed and there is not much left.
If the real variables of oil and sweat are taken into account, is strict sunscreen removal necessary?
Most sunscreens do not need to be removed
You may have already thought about the reason why the experiments mentioned above are so important to our daily life.Life is not realistic enough. A very important factor is that it is almost impossible to sweat in such a cool room for half an hour, so it is impossible to test the effect of sweat and sufficient sebum secretion on the “firmness” of sunscreen. .
There are really some researchers who specifically study the effect of sweating on sunscreen .
A group of Danish scientists made a “human sweating skin simulator” with a multi-layer structure by linking a piece of material specially designed to imitate the human skin base and simulating sweat conduits. “.
Utilizing these devices, they performed in vitro sun protection factor (SPF) measurements, optical microscopy, ultraviolet (UV) measurements “before,” “during,” and “after a sweat.” Reflection imaging and CARS microscopy  were used to evaluate the distribution of sunscreen on the “skin”, as well as the sun protection performance.
The picture above shows the “human sweating skin base simulator” made by the team of Danish scientists, on which sunscreen (filmed) is covered and observed with a microscope / Keshavarzi, F, Knudsen , NØ, Brewer, JR, et al. In vitro skin model for characterization of sunscreen substantivity upon perspiration. Int J Cosmet Sci. 2021; 43: 359– 371.
Experimental results show that sweat reduces the thickness of the film formed by sunscreen and redistributes sunscreens on the skin, both of which are major mechanisms responsible for reduced sun protection performance.
For example, here is an electron microscope image of how sunscreen changes during and after sweating. Picture d is the sunscreen after the sweat has dried, which is completely different from when it was first applied in picture b, becoming thinner and more uneven.
a-Realistic skin substrate without sunscreen in the above picture; b-Realistic skin substrate just applied with sunscreen; c-Applied after 20 minutes of sweating Microscopic image of sunscreen; d – Image of sunscreen redistributed after evaporation of sweat from the same site / Keshavarzi, F, Knudsen, NØ, Brewer, JR, et al. In vitro skin model for characterization of sunscreen substantivity upon perspiration. Int J Cosmet Sci. 2021; 43: 359–371.
Meanwhile, on the effect of sweating on sunscreen on the skin, scientists concluded that the greater the amount of sweating, the greater the reduction in the sunscreen’s sunscreen properties on the skin. Moreover, the loss of sunscreen performance in some areas can even exceed 50% under “moderate sweating” conditions, and the average loss is more than 10%.
Statistical chart of the difference in SPF measured before and after sweating. The colored rectangles represent the interquartile range (IQR), showing the range of values in the middle 50% (25%–75%) of the data. ; the middle line represents the median, and the numbers next to it show the mean / Keshavarzi, F, Knudsen, NØ, Brewer, JR, et al. In vitro skin model for characterization of sunscreen substantivity upon perspiration. Int J Cosmet Sci. 2021; 43: 359–371.
That is, sunscreen applied to the skin will persist over time, but will reduce residue from wear and tear from daily activities.
The longer you spend outside the home and the more perspiration you’re likely to get home, you won’t actually have much effective sunscreen left on your body. And that doesn’t factor in oily skin.
Why do sweat and oil affect sunscreen residue and film formation?
Here I have to introduce the “structure” of sunscreen.
Effective sunscreen ingredients are usually divided into physical blockers and chemical absorbers, which reflect and absorb ultraviolet rays by using the physicochemical properties of the substance respectively. In addition to these ingredients, sunscreens are also composed of the “carriers” of these active ingredients – they work together to form an “emulsion” to achieve a stable and uniform texture.
Therefore, sunscreens can be divided into two categories according to their ingredients and processes: one is oil dispersed in water, called “oil-in-water” type, which has a certain hydrophilicity; For water dispersed in oil, called “water-in-oil” type, it dissolves more easily in oil.
In 2022, a relatively new paper studies the persistence of sunscreens , building a functional model that takes into account daily indoor and outdoor activities. Within 8 hours, there was a very noticeable drop in sunscreen residue. By the eighth hour, only about a fifth of one of the sunscreens was left.
Sunscreen retention on skin as a function of time / N. A. Monteiro-Riviere, K. Wiench, R. Landsiedel, S. Schulte, A. O. Inman, J. E. Riviere, Safety Evaluation of Sunscreen Formulations Containing Titanium Dioxide and Zinc Oxide Nanoparticles in UVB Sunburned Skin: An In Vitro and In Vivo Study, Toxicological Sciences, Volume 123, Issue 1, September 2011, Pages 264–280
So, don’t underestimate the wear and tear of sunscreen in your daily activities. After 8-9 hours of sunscreen, water + facial cleanser is enough for basic facial cleansing.
Some people may feel that the facial cleanser is not clean, there will be residues, and the face will rot.
What remains on the skin may be mainly UV blockers in sunscreens. For example, common zinc oxide is safe even if a small amount remains on the skin, it will not enter your hair follicles, and it will not be absorbed .
Young people wash their faces with water at the sink / Visual China
On the contrary, excessive cleansing, facial cleanser, and cleansing oil may cause certain damage to the skin barrier, including but not limited to weakening the surface barrier structure and killing beneficial microbial flora , causing hypolipidemic skin disease  and so on.
How to wash the sunscreen you bought
We recruited 5 volunteers to actually test 5 sunscreens that are popular and well-reputed on the market today. Five volunteers were asked to apply sunscreen to their forearms with one of the sunscreens.
At the same time, in order to avoid that everyone sitting in an air-conditioned room during the day will affect the experimental results, they were also arranged to go out for a walk in the sun for more than 30 minutes in the afternoon, or exercise in the gym1 hours of exercise.
Photographs were taken with a UV camera  just 30 minutes after applying sunscreen, 4 hours after applying sunscreen, and 8 hours after applying sunscreen.
The experimental results are as follows:
The first column of the image is a control image with one forearm applied sunscreen for 30 minutes and the other without. If you feel that the contrast is not obvious, you can pay attention to the dividing line between color and luster on the volunteers’ wrists: due to the reflection or absorption of UV rays by effective sunscreen ingredients, the part with sunscreen will look darker than the part without sunscreen, and at the same time Parts have brighter reflections.
The second and third columns are sunscreen after 8 hours of sunscreen work (activity), using tap water, pure amino acid cleanser, and makeup remover respectively. Residual level comparison.
It can be seen that compared with washing with water, the effect of washing with cleanser is still significantly different: washing is more “clean”. However, there is no significant difference between using amino acid cleanser and washing with makeup remover, and the effect is not much different from the original skin.
Woman is moistening a cotton pad / Visual China
So, from our test results, if you’re using a sunscreen that’s not specifically labeled as waterproof (usually labeled “after-bath SPF”), and you don’t set your makeup, you’re basically There is no need for special makeup removal, just normal cleaning; there is no need to choose products with stronger cleaning power and wash your face with more force for this purpose.
It is also necessary to talk about a very popular method on the Internet to “distinguish whether sunscreen needs to be removed”: put a few drops of the sunscreen you are using into a glass of water, stir and watch Whether it can form an emulsion, or will there be obvious “oil-water separation”. If there is obvious “oil and water separation”, it is necessary to remove makeup specially.
Is this method really accurate? See also the results of our experiments with the 5 sunscreens above:
It can be seen that L’Oreal and FANCL have obvious “oil-water separation”. Mistine has a moderate water-soluble effect, while Biomel and Anfast can almost all form an emulsion (a small amount can be seen in Anfast. white suspension).
This obviously doesn’t match the results of our first experiment – whether these sunscreens need to be removed is not directly related to whether they create a “lotion” effect when mixed with water. Plus, we’ve verified that these sunscreens basically don’t require a special makeup remover, no matter what they look like in water.
However, if you still want to use a special makeup remover to wash off the sunscreen, you need to choose according to your skin type. Generally speaking, if you do not have “great oily skin”, it is recommended to choose a cleansing oil, which can reduce the dryness and dehydration of the skin caused by washing; for you .
Photo Editing: Eight Feet
Content editor: Mingyu
WeChat Editor: Twelve
Chen, W., He, M., Xie, L., & Li, L. (2020). The optimal cleansing method for the removal of sunscreen: Water, cleanser or cleansing oil?. Journal of cosmetic dermatology, 19(1), 180–184.
Keshavarzi, F, Knudsen, NØ, Brewer, JR, et al. In vitro skin model for characterization of sunscreen substantivity upon perspiration. Int J Cosmet Sci. 2021; 43: 359 – 371.
The Coherent Anti-Stokes Raman Scattering Microscope, a professional scientific instrument, can perform detailed measurement of the refractive index of a sample
N. A. Monteiro-Riviere, K. Wiench, R. Landsiedel, S. Schulte, A. O. Inman, J. E. Riviere, Safety Evaluation of Sunscreen Formulations Containing Titanium Dioxide and Zinc Oxide Nanoparticles in UVB Sunburned Skin: An In Vitro and In Vivo Study, Toxicological Sciences, Volume 123, Issue 1, September 2011, Pages 264–280
Zheng Zhizhong, Li Li, Liu Wei, Wu Yan, Xiang Leihong, Lai Wei & Ju Qiang. (2017). Correct skin cleansing and skin barrier protection. Clinical Dermatology Magazine (11), 824-826. doi: 10.16761/j.cnki.1000-4963.2017.11.027.
 Fan Yi. (2019). The effect of excessive cleaning on hypolipidemic eczema. Chinese Journal of Clinicians (02), 220-222.
Using a UVLOOK camera purchased online
Using OLAY Amino Acid Cleansing
Using Bioderma Makeup Remover
 Zhao Xiaoyu. (2020). Unlock the correct way to remove makeup. China Cosmetics (07), 109-111.
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