It might come as a surprise to some of you, but your skin’s topmost layer (or, the stratum corneum) is mildly acidic in nature. These slightly acidic layers of your skin barrier forms what we call, the ‘acid mantle’. The acid mantle not only regulates key epidermal functions such as barrier regeneration, but also plays a critical role in maintaining physiological microbiota. In this article, we will discuss why skin pH balance is important and how you can restore it.
So, what is pH and how does it apply to skincare?
Skin pH is a term used to measure the degree of acidity or alkalinity in the stratum corneum. It measures on a scale ranging from 0 to 14, where 7 is considered neutral (neither acidic, nor alkaline). A reading below 7 indicates that the substance being measured is acidic, and anything above 7 is alkaline.
Normal skin surface pH (ss pH) is somewhat acidic, and falls in the range of 4.5 and 5.5.
Maintaining the acidic state allows the skin to resume its barrier functions; from skin repair, to inducing epidermal differentiation and reversing the chain reaction that leads to inflammation. However, in contrast to skin surface, the underlying layers of the epidermis maintains a near-neutral pH (7–9). This creates a steep pH gradient of 2–3 units between the skin surface and underlying epidermis and dermis.
Research has shown that any changes made to the skin surface pH (ss-pH) can trigger or exacerbate existing skin conditions, such as acute eczema, contact dermatitis or even acne.
While it is rather uncommon for the skin surface to become too acidic, alkalinity on the other hand, is a greater concern. The repeated use of alkaline cleansers, detergents and even hard water (pH 8.0) can potentially disrupt your skin’s pH balance. This also means that skin surface that is too alkaline, will be more dry and sensitive. Over time, if not corrected, your skin will be more likely to exhibit signs of aging.
So, how much acidity is tolerable?
Next, we move on an important question. Say you’re using an AHA (alpha hydroxy acid) exfoliant with a pH of 3.5, is it safe to use? To answer this, it is important to remind ourselves that our skin leans towards the slightly acidic end of the pH scale. Therefore applying mildly acidic products are generally well tolerated. In fact, regular use of exfoliators reinforces the acid mantle and encourages healthy skin cell turnover and regeneration. But always do a patch test to check for sensitivities.
Remember, with alpha hydroxy acids, the lower the pH, the more exfoliating it will be (as long as it is within safe, skin-tolerable levels).
Great, so can I use lemon?
The next question is, how low can you go with the pH? For example: can you apply pure lemon juice or any other citrus fruit directly on your skin? Short answer: no.
This is based on several reasons. Firstly, you can’t measure the exact potency of a lemon. But here’s what we know already: on average, lemon has a pH of 2.2 and contains about 5-8% citric acid and 0.04% ascorbic acid. Aside from the high concentration of citric acid found in lemon at a known skin-sensitizing pH, the bigger concern would be on the potential risk of phytophotodermatitis. This is a phototoxic reaction that presents as painful skin lesions upon exposure to UVA radiation. Considering all aspects, I don’t recommend that you use lemon juice directly on your skin, instead look for safer AHA alternatives to brighten up your complexion.
What about mild pH changes?
Research has shown that mild pH changes to the skin surface pH can be corrected within 2–6 hours. However, repetitive washing of your skin using alkaline soaps and detergents can disrupt the balance of the acid mantle and once damaged, it can take even up to 14 hours to be restored.
While this may not be a matter of concern for those with healthy skin, it is something you should look into if you are suffering from inflammatory skin conditions such as acne or eczema. In such instances, it is best that you use skincare products within a pH range of 4.7 to 5.5.
Developmental changes in skin pH balance
There are age-related changes in pH that occur during a person’s lifetime. This can be divided into four phases (as adapted from Fluhr and Elias).
- Newborn period: the acid mantle ‘just’ begins to form. During this phase, the stratum corneum displays a near-neutral or slightly alkaline surface pH. However, with time, there is a steady decline noted in the pH — the extent of which depends on the body site and region. It is generally observed that the infant’s cheeks and extensor surfaces (including forearms, forehead and buttocks) are more prone to inflammatory skin conditions such as eczema and diaper dermatitis. This is why your newborn’s pediatrician may have recommended some guidelines to help minimize exposure of irritants, as well as to keep moisture levels under control. Not surprisingly, this can be done by putting simple measures in place, such as avoiding harsh cleansing products, keeping the surface dry and the use of barrier creams to further protect your baby’s delicate skin.
- Childhood period: At puberty, your skin will take time to adjust to the changes brought about by the fluctuating hormone levels. In particular, the apocrine glands which are triggered in response to androgens. This in turn leads to a shift in pH balance, thus making their skin more susceptible to acne (skin is more alkaline during this phase).
- Adulthood period: this is when the stratum corneum is most acidic.
- Aging period: once again, a spike in the pH is noted (and the stratum corneum becomes more alkaline). As we age, our acid mantle becomes weaker and more prone to infections, as well as other inflammatory skin conditions.
Your skin surface is more acidic when you’re younger. This is why it is better protected, looks more healthier, and heals faster.
Causes of pH Imbalance
Recognizing the factors that can affect skin surface pH is an important step in preserving the acid mantle. Several factors, including both endogenous and exogenous elements can influence your skin pH. These include: age, anatomic site, genetic predisposition, skin moisture, sebum and sweat. This also explains some of the age-related transitions (as discussed above) that occur during a person’s life.
Some interesting facts about skin pH:
- Anatomic sites with varying pH levels. The apocrine sweat glands located under the arms and around the groin is associated with the higher skin pH in these areas. The alkaline environment then allows odor-producing bacteria to thrive.
- Pigmented skin has lower pH (more acidic) when compared to persons with lighter skin.
- Men in comparison to women, have lower skin surface pH (more acidic).
- Excessive sweating can increase skin surface pH.
- Aging increases skin surface pH. As you age, your skin’s pH becomes more neutral, and thus more susceptible to wrinkles, sun damage, smoking, and other pollutants.
Studies have reported superior stratum corneum integrity and lower skin surface pH among darker skinned individuals.
Water and skin surface pH. Does it even matter?
It is not just the skincare products that you use, that influences your skin pH. According to a study published in the International Journal of Cosmetic Science, even plain tap water can shift the balance in skin’s acidic mantle.
As highlighted in their research findings, the European tap water, which has an average pH of 8.0, can increase the skin’s pH levels post-cleansing. The effects of which can last for up to 6 hours before returning to ‘normal’ levels.
Now you might be wondering, who will this affect the most? To narrow it down, if you have highly reactive skin or conditions such as eczema and rosacea, the pH level of the water might be something to look out for. You could either invest on shower filters or use lipid-free cleansers, micellar waters for cleansing to minimize any potential irritation.
There are some exceptions to this rule: sunscreens and heavy moisturizers are sometimes formulated at near neutral pH (7-7.5).
This could be for two reasons. Firstly, sunscreens will not be able function at low pH levels and more importantly, for mineral sunscreens, you would want your sunscreen to sit on top of you skin to block out the UV rays.
Tips to restore skin pH balance
- Look for “pH-balanced” products in your skincare. This means, you’re going to opt for gentle cleansers, that have pH levels ranging between 4.7 to 5.5. You can check out our recommendations for dry and oily skin.
- Alternatively, you can use toners. These are typically formulated with either neutral or slightly acidic composition. This helps to balance your (slightly) alkaline skin, post-cleansing. Look for toners with acid blends such as lactic or glycolic acid to exfoliate, or soothing toners. As a general guide, it is best if you can avoid toners that contain alcohol as it can trigger further skin issues and may also strip your skin of moisture.
- Antioxidants. After cleansing and balancing the acid mantle with a toner, apply the antioxidant serums of your choice. This will help strengthen the skin barrier as well as protect the skin from external aggressors.
- Moisturizing is the key. It will help restore and maintain the integrity of the skin’s acid mantle. Look for moisturizers with emollients, ceramides and hyaluronic acid to support skin’s moisture barrier. You can check out our recommendations for dry, oily and acne-prone skin.
How to layer skincare by pH
Typically, in terms of texture, skincare products should be applied from thinnest to thickest. However, in context of pH, you can apply them in order of lowest to highest pH level.
Where can you find this information? Well, some brands provide this information on their product label, or on their website. If this doesn’t work, you can even contact the brand and inquire about it.
It is recommended that you apply the acidic products before the neutral ones when layering skincare products.
Is there a wait time necessary in between product applications?
If the two products fall in the same pH range, you can apply them at the same time. However, if there is a notable difference in the pH, you could wait for 20-30 minutes before layering it with the other product. Or better still, alternate the two products between your morning and evening rituals.
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