EVERYTHING YOU NEED TO KNOW ABOUT SKIN PH

Published January 3, 2024

When pH is mentioned, the first thing that comes to mind is usually distant memories of chemistry classes at school. But did you know that pH plays a key role in the proper functioning of cells and organs in the human body? And that the skin's pH is an important thing to consider when looking to maintain healthy, well-balanced skin?

This article will tell you everything you need to know about skin pH. We'll take a look at the role it plays, what can cause it to change, and how FILORGA's cosmetic treatments help maintain it to make sure your skin stays as radiant as ever.

WHAT IS PH?

Invented by Danish chemist Soren Sorensen in 1893, the concept of pH (or “potential of hydrogen”) is an indicator of the acidity or basicity of a solution or liquid. pH has no unit, only a number between 0 and 14.

- Values below 7 indicate an acidic solution.

- Values greater than 7 indicate a basic or alkaline solution.

- If the pH value is 7, the solution is considered neutral. For this last measurement, pure water at a temperature of 25°C is used as the reference.

Here are some common examples of pH levels:

- Gastric acid: 1–1.5

- Orange juice: 3.5–4

- Black coffee: 5

- Milk: 6.5–6.8

- Seawater: 7.5–8.4

- Bleach: 12.5

- Detergent: 13–13.6

Incidentally, an acidic substance like orange juice will never harm the digestive tract. After all, it passes through the stomach, which contains gastric acid, one of the most acidic substances in existence. An acid is fine as long as... it stays in the stomach.

In nature, living organisms require a certain pH to live and thrive. For example, some plants do better in acidic soils (pH between 4 and 6.5), while others need basic or limestone soils (pH 7 to 8).

The same goes for humans, for whom pH is vitally important.

PH IN THE HUMAN BODY 

The pH of human organs is carefully regulated and ranges from 1 to 8. Anything outside this range means that all the different enzymes in the body can't activate, which can block certain reactions that are essential to our metabolism. The body therefore needs to maintain the pH of its organs within their optimum operating range at all times.

For example, the respiratory and renal systems constantly regulate the pH of our blood to keep it between 7.35 and 7.45, because any variation (particularly towards acidosis) can potentially be fatal.

Another example, referenced above, is the empty stomach, which has a highly acidic pH of 1 to 1.5. This is essential for pre-digestion and protection against bacteria. Low acidity can lead to gastrointestinal infections, while excess acidity (below 1 pH) can result in gastric ulcers. 

The pH of certain organs can also change slightly over the course of the day. Tears, for example, are more acidic in the morning when they come from an unopened eye than later in the day (average pH 7.25 versus 7.45).

WHY DOES SKIN PH MATTER?

The skin's surface is covered by a hydrolipidic film. This film, also known as the acid mantle, has a slightly acidic pH of between 4.5 and 5. 

This acidic pH promotes the development of the “good” bacteria in the skin microbiota and forms a protective barrier against pathogenic bacteria present in the environment. It also protects the integrity of the stratum corneum by regulating the enzymes involved in desquamation, which is the elimination of dead cells from this surface layer of the epidermis.

When there is an imbalance in the skin's acid mantle, certain problems can arise, such as:

- Irritation;

- Dryness;

- Infections;

- Acne.

So maintaining a balanced skin pH is essential to help maintain the skin barrier and to help the skin defend itself against external stresses, while also maintaining the levels of hydration and suppleness required for healthy skin.

WHAT CAN AFFECT SKIN PH?

The skin's natural pH can be influenced by a number of both endogenous (i.e. from within the human body) and exogenous (i.e. from outside the body) factors. The following are the most significant:

AGE

Studies have shown that surface pH values in newborns are relatively neutral (around 7), decreasing to around 5.5 during the first 4 days of life. This pH will gradually stabilize to between 4.5 and 5 as we enter adulthood, with localized variations during adolescence (with the appearance of acne on the face, for example).

In people aged between 18 and 60, skin pH shows little variation and generally remains constant over most of the body.

In contrast, it tends to increase among the elderly.

SEX AND ETHNICITY

People with darker skin have a lower skin surface pH than people with lighter skin. A recent study also showed higher skin pH in women (5.6) than in men (4.3).

COSMETIC PRODUCTS

One of the key external factors that influence skin pH is cleansing. In general, the following can be observed:

- A significant increase in pH for at least a few hours after cleansing the skin with alkaline soaps (pH 10.5–11.0).

- A lesser increase, and for a shorter period of time, after using tap water or facial cleansers formulated with the same pH as the skin.

- A very minor increase when using formulas containing surfactants.

In each case, the increase in pH is reversible, and values return to normal after a few minutes or hours.

DOES PH INFLUENCE SKIN TYPE?

Oily skin generally has a less acidic pH than the norm, which favors the proliferation of the bacteria responsible for acne. On the other hand, dry skin tends to have a lower pH value, which can lead to irritation and itching. Combination skin features areas with different pH levels.

So it's essential to maintain a balanced skin pH to keep it healthy and radiant. This is why Laboratoires FILORGA's experts recommend using skincare products that are specifically designed for each skin type. 

FILORGA’S TREATMENTS PROTECT THE SKIN’S PH 

All our treatments undergo rigorous dermatological testing to ensure that they are totally skin safe and do not cause any adverse reactions under normal conditions of use. They are suitable for sensitive skin, and their pH is neutral for the skin, meaning it matches its natural pH.

The pH of our creams is also adjusted to suit the active ingredients to ensure optimal results. For example:

- AHAs (alpha hydroxy acids), used as exfoliants or moisturizers, need to be added and maintained at a highly acidic pH.

- Pure vitamin C rapidly oxidizes (or breaks down) when exposed to the oxygen in the air. It's a highly unstable natural acid (scientifically known as ascorbic acid) that also needs to be formulated at an acidic pH of around 3.5. But its derivatives can have higher pH values because they're stabilized. This is the case for ascorbyl glucoside, which is found in HYDRA-AOX [5]. The glucoside helps to “protect” vitamin C from oxidation.

- Gluconolactone must be added at a pH below 6 to enable it to be converted into gluconic acid, which is the active form of this exfoliant.

pH can also have a significant effect on the feel of a product; some gelling agents require a specific pH in order to work. An inappropriate pH (or a change in pH over time) can alter the product's viscosity and, consequently, its feel.

To sum up, pH is an essential building block of the skin barrier, and it's therefore crucial to use skincare products that respect the skin's pH. It's also important to keep in mind that the skin is naturally acidic, so a product that is pH-neutral for the skin does not mean that it has what would be considered a neutral pH value. As mentioned above, this means a pH of between 4.5 and 5.

Sources:

Proksch E. pH in nature, humans and skin. J Dermatol. 2018 Sep;45(9):1044-1052. doi: 10.1111/1346-8138.14489. Epub 2018 Jun 4. PMID: 29863755.