Ch.03, Exfoliating Acids
Back in ancient Egypt, women used sour milk, rich in lactic acid, to improve the appearance of their skin.
Though we don't recommend this ancient practice today, fear not! A contemporary path to smoother and brighter skin awaits you: cosmetics enriched with exfoliating acids. As there seems to be a bit of confusion about what they are and what they do, this chapter will try to outline all the basics.
Why exfoliate?
Our skin naturally sheds old cells as a part of its renewal process, a phenomenon known as skin cell turnover or desquamation. For your skin to remain healthy, this turnover, which typically takes two to three weeks, needs to be supported. Exfoliation mimics and aids this natural process, ensuring that fresh, healthy skin continually surfaces (1).
However, factors like aging, hormones, environmental stressors, diet, and lifestyle can slow down this process. When this happens, dead skin cells can accumulate, leading to clogged pores, blemishes, dehydration, and a lackluster appearance, characterized by dull, scaly, and rough skin. But don’t worry, by maintaining a consistent exfoliation routine, you can prevent these issues and help your skin return to a healthy turnover rate (2).
Exfoliation can be achieved using two main methods: chemical and physical.
Physical exfoliation involves tools that mechanically remove loose skin cells from the skin's surface. It's vital to opt for gentle tools like a soft brush or konjac sponge, rather than aggressive or coarse tools, such as gritty scrubs, which might lead to microtears in the skin.
Chemical exfoliants penetrate deeper, dissolving the bonds—or the "glue"—between skin cells to allow for easier removal. The process targets the top layer of the skin, which is already dead, so it's not as harsh as it might sound. Once the chemical exfoliators help kick out those old cells, your skin can benefit from a brighter and smoother texture relatively quickly. Moreover, when incorporated as a consistent treatment, these exfoliants can reduce age spots, even out skin tone, and diminish wrinkles and fine lines. Their anti-aging effects are particularly profound due to the increased skin cell renewal and the improvement in skin texture and clarity they offer.
Consider the relationship between physical and chemical exfoliation as a partnership. Physical exfoliation, much like sweeping your front porch, clears the top layer of your skin, preparing it for guests. Meanwhile, chemical exfoliation delves deeper, addressing issues beneath the surface, akin to tidying up the interior of your home.
The 3 types of exfoliants
Exfoliating acids can be divided into 3 overall groups called AHAs, BHAs, and PHAs - popular terms you have probably heard of. The differences between them are characterized by their molecular size and overall function which leads to different skin benefits. The bigger molecular sizes work on the surface levels, whereas smaller ones are better able to penetrate skin to treat clogged pores and mild breakouts (3).
Here’s a brief description of each type:
1. Alpha-hydroxy acids (AHAs)
AHAs are a group of water-soluble acids that are naturally found in food and commonly used as active ingredients in skincare. The AHA category includes glycolic acid (found in sugar cane), lactic acid (from milk), malic acid (found in fruits), mandelic acid (found in almonds), and citric acid (found in lemons). AHAs work by breaking down the ‘glue’ that holds together cells at the surface of the skin, which increases the skin’s cell renewal rate and helps achieve brighter, healthy skin (1,3,4).
Glycolic and lactic acids, the main alpha-hydroxy acids, have undergone extensive research over decades. Various studies support their ability to enhance skin texture, boost hydration, increase skin thickness, stimulate collagen and reduce the appearance of wrinkles and uneven pigmentation (2). Thus, AHAs are great exfoliating agents, but also work as good anti-aging ingredients.
AHAs are versatile for all skin types, but their effectiveness and gentleness are influenced by molecular size. Lactic, malic, and mandelic acids, having larger molecules, penetrate the skin less aggressively, making them gentler and ideal for sensitive skin. In contrast, glycolic acid, with its smaller molecule, penetrates more deeply, offering potent exfoliation suitable for non-sensitive skin.
2. Beta-hydroxy acids (BHAs)
BHAs are oil-soluble acids and because of their oil-loving structure, they can penetrate deeper into the pores rather than act on a superficial level. Inside the pore, BHAs work by helping remove excess oil and sebum from the skin.
Salicylic acid, the most notable BHA, holds a prominent position in skincare. Its multifunctional attributes encompass anti-inflammatory and antibacterial properties. Extensive clinical trials have validated its efficacy, particularly formulations containing 0.5% and 2% salicylic acid for acne treatment (2). Therefore, salicylic acid is ideal for oily, blemish-prone skin and can also help treat inflamed pimples and unclog pores. However, it should be avoided during pregnancy or if there is a known allergy to aspirin (3).
Salicylic acid can be sourced from natural origins like willow bark and wintergreen oil or synthesized in a laboratory setting.
3. Poly-hydroxy acids (PHAs)
PHAs are chemicals with a larger molecule size when compared to AHAs and BHAs. Because of this, they only work on the top skin surface level where they can provide similar results to other chemical exfoliants but with far fewer irritation responses. They are so gentle on the skin that they don’t cause sun sensitivity and therefore are a great option for dry or sensitive skin types.
The PHA category in skincare usually includes two molecules: gluconolactone and lactobionic acid. Although PHAs have been less researched, some studies have shown similar anti-aging benefits to AHAs. Moreover, PHAs have demonstrated an ability to enhance the skin barrier function by increasing moisture levels and cell turnover (3).
| Type | Benefit | Penetration | Research | Gentleness |
|---|---|---|---|---|
| AHAs | Anti-age | Upper layer | ★★★ | ★★ |
| BHAs | unclogging | Deeper layer | ★★ | ★ |
| PHAs | Anti-age | Upper Layer | ★ | ★★★ |
The 2 things to look for
After choosing your desired exfoliating acid(s), two crucial factors are pivotal when assessing their effectiveness:
Concentration: Research indicates that the ideal concentration for AHAs ranges between 4-10%. It is recommended that concentrations beyond this is administered professionally. For BHAs, the sweet spot is 0.5-2%. Given PHAs' gentler nature, a 10% concentration is optimal. For those new to exfoliating acids, starting with lower concentrations is advised to prevent irritation.
pH Level: AHAs/PHAs products should have a pH of 4 or lower for optimal results. While salicylic acid typically follows this guideline, some research suggests it can exfoliate effectively with reduced irritation at a neutral pH of around 6.55.
How to use exfoliating acids
Navigating skincare exfoliation can seem daunting. Here are some insights for seamless integration into your skincare routine.
Apply sunscreen
Using AHAs can make your skin more sun-sensitive due to their ability to exfoliate the top layers of skin cells. Even if you apply AHAs only at night, it's crucial to use broad-spectrum sunscreen daily and limit sun exposure. While BHAs and PHAs don't notably heighten sun sensitivity, maintaining consistent sunscreen use is always a good practice.
Consider frequency
The appropriate frequency of application is contingent upon your skin type and the product's concentration. For products with AHA concentrations exceeding 10%, a weekly application is advisable. However, formulations with milder concentrations can be applied multiple times throughout the week. Individuals with oily skin may find daily application suitable, whereas those with dry or sensitive skin might best utilize the product on alternate nights or with decreased frequency to achieve optimal results. If you have sensitive skin or you’re just starting, start with low concentrations, see how your skin responds, and slowly increase the concentration and frequency of use.
Monitor reaction
A slight tingling sensation upon application can be standard with some exfoliating acids. However, prolonged redness, itching, or burning is a sign that the product might be too strong, or your skin needs more time between applications. If this happens pause using the exfoliating acid and focus on repairing your skin barrier with nurturing and moisturizing products.
Cleanse and apply
Start by cleansing your face to ensure that the exfoliating acid can effectively penetrate the skin without any barriers of dirt or makeup. After cleansing, apply your exfoliating acid, which might be a serum or toner formulated with AHA, BHA, or PHA. It's wise to give the acid a few minutes to work on your skin, allowing it to penetrate effectively and reducing the potential for interactions with subsequent products. Once you've waited, continue with your skincare routine, applying a hydrating serum, moisturizer, or any other products you regularly use.
Acids’ friends
Exfoliating acids can cause temporary skin sensitivity or dryness. To counteract these effects, it's advisable to pair them with hydrating and soothing ingredients such as hyaluronic acid, glycerin, ceramides, allantoin, niacinamide and aloe vera. These ingredients not only enhance the skin's moisture barrier but also alleviate potential irritation, ensuring that the skin remains healthy and calm with regular exfoliation.
Acids’ enemies
Combining ingredients with strong exfoliating properties or low pH values with exfoliating acids may increase skin irritation risks. These include:
Vitamin C (L-Ascorbic Acid) has a low pH, so pairing it with exfoliating acids might cause discomfort. A balanced approach would be using one in the morning and the other at night.
Retinol/Retinoids, when mixed with exfoliating acids, can be particularly harsh. It's advisable to either alternate nights or use one in the daytime and the other at nighttime.
Benzoyl peroxide can intensify the effects of AHA/BHA, potentially causing skin dryness and irritation. Likewise, pairing chemical exfoliants with gritty scrubs can lead to over-exfoliation and increased skin sensitivity.
CHEAT SHEET
Our skin naturally gets rid of dead cells, a process known as desquamation. However, as we age and due to environmental factors, this shedding slows down. This can lead to issues like blemishes and dull skin. Exfoliation can help combat this.
There are 2 primary methods for exfoliating the skin:
Physical exfoliation, which involves the use of tools like brushes and sponges to mechanically remove dead skin cells on top surface.
Chemical exfoliation, where acids penetrate into the dermis and work to dissolve the bonds between dead skin cells so they can come off easily.
There are 3 exfoliating acid types:
AHAs (Alpha-hydroxy acids) are water-soluble acids derived from fruits and milk. Due to their large molecular size, they primarily act on the skin's surface. Among them, glycolic and lactic acids are the most researched and have showcased their ability to enhance skin texture, stimulate collagen and reduce and hyperpigmentation. For best results, an AHA concentration of 4-10% is recommended, with higher levels best administered by professionals.
BHAs (Beta-hydroxy acids) are oil-soluble acids that penetrate deeply into pores to eliminate excess oil and sebum. Salicylic acid, the most renowned BHA, is also known for its anti-inflammatory and antibacterial properties making it ideal for oily and acne-prone skin. It is effective in concentrations ranging from 0.5-2%.
PHAs (Poly-hydroxy acids) have been catching attention in skincare as the gentler alternative to AHAs and BHAs. Because of their larger size, they only work on the skin's surface. Research indicates that prominent PHAs, like gluconolactone and lactobionic acid, can offer anti-aging benefits akin to AHAs. Given their mild nature, a 10% concentration is optimal, and they pose no sun sensitivity risks.
Using exfoliating acids can lead to skin sensitivity. To combat this, it's wise to include hydrating and calming ingredients like aloe vera and hyaluronic acid in your routine. Do not layer exfoliating acids with vitamin C, retinoids, or benzoyl peroxide as this increase risk of irritation.
Questions & Answers
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It is normal to feel a tingling sensation when using exfoliating acids at high concentrations or for the first time. However, if you experience burning, redness, irritation, or inflammation, discontinue use.
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Enzymes from pineapple (bromelain), papaya (papain), and kiwifruit (actinidin) are believed to have the potential to break down bonds between skin cells. However, studies that support enzyme efficacy are still scarce compared to studies supporting exfoliating acids.
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Exfoliating acids (AHA, BHA, PHA) differ from azelaic acid in the mechanism of action. Both can help reduce sun spots and hyperpigmentation, but exfoliating acids work by gently removing the top layers of skin cells, while azelaic acid works by inhibiting the action of an enzyme necessary for pigment production on the skin.
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Masks typically contain higher concentrations of acids, making them potent and best suited for use once every 1-2 weeks. Serums, although concentrated, possess a thicker consistency that provides both hydration and a gradual release of the acid, thereby minimizing potential irritation. In contrast, toners have a watery consistency, causing them to evaporate rapidly. This quick evaporation can sometimes lead to increased skin dryness and potential irritation
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Yes, but with caution. Skincare products combining multiple acids are typically formulated to maximize benefits while minimizing irritation, ensuring the concentrations are balanced. However, if you layer separate products with distinct exfoliating acids (e.g., a salicylic acid toner, glycolic acid serum, and lactic acid moisturizer) in one routine, you may risk over-exfoliation and damage to the skin barrier.
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Yes, but given that exfoliating acids, especially AHAs, heighten sun sensitivity, it's essential to use a broad-spectrum SPF and reapply every 2-3 hours.
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The skin around your eyes is thinner and more delicate compared to other facial areas. Using exfoliating acids around the eyes is a great way to reduce crow’s feet and fine lines appearance, but you should only use products specifically formulated for this area.
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1. Fu, V. & Lu, G. Skincare decoded : The practical guide to beautiful skin. (2021).
2. Imhof, L. & Leuthard, D. Topical Over-the-Counter Antiaging Agents: An Update and Systematic Review. Dermatology 237, 217–229 (2021).
3. Mahto, D. A. The Skincare Bible: Your No-Nonsense Guide to Great Skin. (2018).
4. Clifford, P. Alpha Hydroxy acids in Skincare. (1996).
5. Merinville, E., Laloeuf, A. & Moran, G. Exfoliation for sensitive skin with neutralized salicylic acid. Int. J. Cosmet. Sci. 23, 115–119 (2008).