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How pH affects AHAs and BHAs in skincare formulations

The pH scale is a measure of how acidic or alkaline a substance is, on a scale from 0-14. Most people think of pH as a fixed measurement, for example battery acid is pH 0, tomato juice is pH 4, water is pH 7, and so on. However the true pH of a substance often exists as a range, depending on many external factors. Water is considered neutral on the pH scale, but natural bodies of water are often alkaline due to carbonates in bedrock, and when it’s polluted, water can become acid rain.

Small adjustments in pH can make a big difference, both in nature and in skincare. In this post, we’ll review how pH affects alpha and beta hydroxy acids in skincare formulations, and how to maximize results by focusing on pH levels.

What is the pH scale?

ph scale diagram

Christinelmiller, CC BY-SA 4.0, via Wikimedia Commons

The pH of a substance is determined by the concentration of free hydrogen ions it contains, relative to distilled water (true neutral). Acids release these ions, so the more acidic a substance is, the more ions it will produce. The scale increases and decreases 10x for each number. So if pure water has 0 ions, then something that is pH 6 will have 10, while pH 8 will have 1/10. At the far ends of the scale, a strongly base substance such as lye has 1/10,000,000 ions, while very acidic substances like battery acid, pH 0, have 10,000,000 ions.

Substance

pH rating

Free hydrogen ions

Lye

14

1/10,000,000

Oven cleaner

13

1/1,000,000

Soapy water

12

1/100,000

Ammonia

11

1/10,000

Milk of magnesia

10

1/1000

Toothpaste

9

1/100

Seawater

8

1/10

Pure water

7

0

Milk

6

10

Acid Rain

5

100

Wine

4

1000

Soda

3

10,000

Vinegar

2

100,000

Stomach acid

1

1,000,000

Battery acid

0

10,000,000

Because of the way the pH scale works, there can be a big difference in acidity or alkalinity between two substances that appear very close together. Stomach acid, for instance, is a lot stronger than vinegar. In fact, it’s 10 times stronger, even though they’re right next to each other on the pH scale. If you spill vinegar on your hand, it’s not a big deal. If you spill hydrochloric acid (stomach acid) on yourself, it can cause chemical burns, ulceration, and necrosis.

Our skin and the pH scale

red haired woman with freckles looking at camera

Everything has a pH, even our skin. For most people that’s around 5 to 5.5 pH, or about as acidic as black coffee. Having acidic skin is important for protecting and nourishing our cells. The acidity comes from the acid mantle, a fine barrier made up of skin oil and sweat. While that sounds gross, this barrier protects us by preventing bacteria and dirt from getting in, or water from getting out of our skin.

The specific pH of our skin is dependent on factors like our genetics, environment, and skincare products, and can vary between 4.5 and 6.2 pH. That’s a big difference, and it can make a big difference to our skin’s condition. Weaker acidity means less protection. The bacteria P. acnes, for example, is part of our normal skin microbiology, but when it gets out of control it is a common cause of acne. Studies on the “Effects of pH on biomass” of P. acnes found that it flourished in environments of pH 6 to 6.5, so the weaker the skin’s acid mantle, the more likely you are to experience acne breakouts.

AHAs and BHAs on the pH scale

Alpha and beta hydroxy acids are generally around 3-4 pH, about the same acidity as soda or wine. Salicylic acid, the BHA used in skincare products, is the most acidic at pH 3.0. Lactic acid, an AHA, is the weakest acid, at pH 3.9. However it’s important to remember that even though these numbers seem close, because the pH scale increases tenfold between each number, salicylic acid is around nine times stronger than lactic acid.

How pH affects skincare

woman with soapy hands

Finding the right balance between our skin pH and the skincare products we use is important for getting the best results from the ingredients we use. Our skin pH fluctuates all the time based on other substances it’s exposed to. For instance, after showering in soap (pH 9-10) the pH of skin rises. Studies evaluating the “pH of Bathing Soaps and Shampoos” found that formulations with a high pH caused “ an increase in dehydrative effect, irritability and alteration in bacterial flora.”

A study on the “Relation of pH and Skin Cleansing” found that the increase in skin pH after exposure to higher pH substances lasts a few hours after a single exposure, so if you shower with soap in the morning, your skin pH will have returned to normal by lunchtime. However ongoing exposure can lead to longer term changes to the acidity of your skin. This can be a good or a bad thing. For instance repeated washing with soap will create a higher pH environment, which can lead to dry skin and acne breakouts. Alternatively consistent use of low pH products can help keep your skin pH lower, improving overall skin tone and appearance.

Alpha and beta hydroxy acids are naturally more acidic than skin, and so can contribute to lowering skin pH, especially in leave-on formulations such as moisturizer. This means they can be powerful ingredients for adjusting skin pH to healthier levels — within reason. One of the reasons many people find AHAs/BHAs cause irritation when they first use products with those ingredients is because of their low acidity. The higher or lower any substance is on the pH scale, the more harm it poses to skin. Therefore finding the right balance of skincare pH, relative to your skin’s natural pH, is important to minimize irritation and provide the best effects.

How Qyral products adjust for pH

At Qyral, we take the pH of our products seriously. Mass-market skincare formulations are designed to treat the average person’s skin, so if your skin pH falls outside the 5-5.5 range, you’re more likely to experience negative side effects from AHAs/BHAs and similar ingredients. 

Your skin pH can also affect how well ingredients work. When substances of different pH interact, they change composition by giving up or attracting free hydrogen ions. That’s why you can dilute or neutralize an acid by adding a base. These interactions change the molecule size of the substance. When it comes to AHAs/BHAs in skincare, these changes mean they don’t absorb as well into your skin.

Matching the pH of your skincare formulation to your skin’s natural acidity increases absorption and leads to better results, so that’s what we do! Our Skin Assessment Quiz determines the acidity of your skin barrier by examining your usual skin condition, most common complaints, and overall sensitivity. This lets us choose the right combination of AHAs/BHAs to boost absorption while minimizing irritation. That means maximum results, without any nasty side effects!

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