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by Dr.Yu-Chang Chan 

Acid Skincare is on Trend! Let the dermatologist give you a guide!?

Acne wouldn’t go away; large pores are on display and dead skin cells are piling up, causing dullness and pimples. There is no hope to achieve the dreamy translucent and fair skin. What to do? An acid skincare treatment that can reboot the metabolism of stratum corneum may be an effective solution and that’s why new acid related products are put on the market all the time. How to apply acid to salvage skin condition? Here is the knowledge from the well-known dermatologist Yuzhang Zhan of what is the proper way to use acid products.

Q: Why acid skincare is trending now?

Dr. Yuzhang Zhan:

To speak of acid skincare, everyone comes up with fruit acids. Fruit acid has been used around for about 30 years. Although its popularity has been up and down, it has never faded away. It is very helpful for treating acne, pore and pimple, and there are many people in need of it; so, it has remained its popularity.

The reason why acid can improve acne, pore and pimple is because its mechanism of action to reboot the metabolism of stratum corneum, so that the pores wouldn’t be clogged. When there is acne, it means that the metabolism of stratum corneum is abnormal. Normal stratum corneum sheds off every once in a while, but some people’s stratum corneum can’t function normally and leads to clogged pores, and what’s inside will accumulate and become acne; it is what leads to pimple, and usually comes with the problem of large pores.

In general, the skin can be divided into dry, oily, normal, combination and sensitive skin types. Most people often think that only oily skin is prone to acne or pimple. In deed that oily skin has the problem of excessive sebum production, which may lead to clogged pore. But the truth is, when the skin is too dry, it would also cause abnormal metabolism of stratum corneum and clogged pores. Therefore, acid is not only exclusive to oily skin, but also to other skin types that have problems with metabolism of stratum corneum.

Q: What are the effects of the most common acids, fruit acid, tretinoin, azalea acid, salicylic acid, and mandelic acid? Why mandelic acid is widely used now?

Dr. Yuzhang Zhan: Fruit acid peeling originated from the United States, but it could cause strong irritation reaction, so scientists replaced it with multi-acid peeling, which can reduce the concentration of various acids, decrease potential irritation, and utilize different properties of each acid to tackle problems like pore and acne. The followings are some of the most common acids in the market for acid skincare.



Tretinoin is the most common acid in the early years. It is not irritating when applying on to the skin, but it could easily cause the skin turn dry and sensitive after it’s been absorbed for a few days. According to regulations, it is not allowed to be added to skincare products due its strong effects, so it is mostly obtained from prescription by the doctor, including topical ointment and oral ingot. Tretinoin has a small molecular weight and is water-soluble; it can penetrate deep into the skin. It usually can take effect with a low concentration. The most common concentration of common medicinal tretinoin is around 0.05-0.25. Besides eliminate growing acne and pimple, it also has preventive effect.

- AHA fruit acid

AHA fruit acid is a widely used ingredient in skincare products. It is not particular acid, but a generic term for acid from a variety of natural fruits and vegetables. For example, glycolic acid and citric acid are both a kind of fruit acids. Among them, glycolic acid is the most widely used. It is water-soluble and has a small molecular weight, which can penetrate into deep epidermis layer and even to the superficial dermis layer. However, glycolic acid needs a higher concentration and a lower pH value to penetrate into the deep layer. Otherwise, it is easy to just stay on the surface of the skin, leaving skin itchy, uncomfortable, and irritating immediately. It is important to know if your skin can withstand the concentration and pH value.


- Azalea acid

Azalea acid is mainly used for anti-inflammatory and elimination of existing acnes and pimples. It can penetrate deeper than salicylic acid to the inner layer of the epidermis, so the acne types that it can reduce is deeper than salicylic acid. In addition to help the metabolism of stratum corneum, it also has brightening effect, so it is often used by dermatologists. However, it requires a very high concentration to take effect. Normally, it is a low concentration when used in skincare products, which brings multiple effect but not extremely effective, it is mostly used as a supporting ingredient.

- Pyruvic acid

Pyruvic acid is a product of decomposition of glucose. Most of the energy required by body cells comes from glucose, so pyruvic acid is part of the skin. Its molecular size and effect are similar to glycolic acid. The difference is that it is soluble in both oil and water, so it penetrates faster than water-soluble glycolic acid, but it must be absorbed into the skin and through mechanism of action to take effect. Pyruvic acid usually plays the role of replacing or assisting glycolic acid in acid treatment. 


- Salicylic acid

Salicylic acid is another acid with long history. It is fat-soluble so that it can't penetrate to the deep layers of the skin. It is better for treating acne and pimple on the surface, yet it causes strong immediate irritation like fruit acid.


- Mandelic acid

Mandelic acid is also one kind of fruit acid. It has its own section because it is different from other fruit acids. It is not water-soluble but fat-soluble. The stratum corneum of the skin is also fat-soluble, so mandelic acid is able to stay on the stratum corneum without deep penetration and leading to irritation. And mandelic acid is also the mildest among all kinds of acids, which can also brighten the skin. The molecular weight of mandelic acid is relatively bigger and works well on normalizing the metabolism of stratum corneum. It is suitable for treating acnes and pimples at home without irritation but effective. This is the reason why mandelic acid is very popular now.

Q: Will the use of mandelic acid leave skin thinner?

Dr. Yuzhang Zhan: Not just mandelic acid, basically the use of every kind of acid would not cause thinning skin. Take the strong acid such as tretinoin and fruit acid as example, they may actually make the skin thinner at the beginning. However, since it can act on the deep layers of the skin and stimulate the production of collagen, the skin will become firm, plumped and healthy after long-term use. In the case of a relatively fat-soluble acid that penetrates shallow layer of the skin, such as mandelic acid, it mainly helps the metabolism of stratum corneum, which won't make the skin become too thin and sensitive.


Q: Pimples and acnes show up after using mandelic acid and make skin condition worse?


Dr. Yuzhang Zhan: It may happen briefly when starting mandelic acid treatment for few people, but not to everyone. At the beginning of the treatment, it may feel like that acnes are showing up more and more, it is actually helping diminish the clogged acne. Once sticking to the treatment for a month, the skin will become smoother. Though the use of mandelic acid may induce acne, the inflammatory reaction is not worse than when you’re not using mandelic acid. Not only the time to recover is shorter, but also acne marks would stay shorter.

If you come across a lot of skin problems during the process of mandelic acid treatment, you need to check whether your usage or the skin care products is right. If your metabolism is normal, the need for acid treatment is not strong, but because of excessive usage, it accelerates metabolism of the skin, which could cause scaling. Sometimes scaling problem escalates and leads to peeling of the surface layer of pore. Accidently causing pore blockage when skin is repairing could also provoke acnes and pimples. Therefore, it is recommended that people who do not have too many acnes should pay special attention to the frequency, dosage and concentration of acid to avoid serious scaling reaction.

Q: How to choose mandelic acid?

Dr. Yuzhang Zhan:  For acne-prone skin type, you can choose mandelic acid with higher concentration to enhance the effect on metabolism of stratum corneum. The popular concentration most people prefer is 18%, and the concentration higher than 18% may not lead to a better result. However, if there are multiple skin problems, it is recommended to choose a multi-acid. For example, high concentration is not suitable for acne-prone sensitive skin, which should turn to multi-acid with lower concentration of all kinds of acid to reduce irritation, make it fitting for sensitive skin and allow different kinds of acids to penetrate different skin layers to achieve synergistic effect.


Q: How to use mandelic acid and any details to pay attention to?


Dr. Yuzhang Zhan:   It is recommended to dry the face after cleansing, wait for 1 minute, when there is still moisture in stratum corneum, but the surface of the skin has turn dried. Apply mandelic acid serum directly on the skin, because now stratum corneum is full of moisture, so the acid will stay on the surface layer instead of penetrating too deep. Wait around two or three minutes for absorption of the acid serum, and then add moisturizing products. Normally, after peeling, the skin is a bit dryer than usual, it is recommended to use lotion or cream like moisturizer that can balance oil and moisture, but it is not recommended to use other skin care products contain acid.

Although mandelic acid is mild, but any acid could be a little irritating, and a bit of scaling reaction is normal. However, it is not normal if it continuously shows scaling reaction during treatment and gets worse. Then you should consider to reduce the concentration or extend the frequency of treatment. It can change from every 2 days to every 3 or 4 days.