The pH of Skin

The surface of human skin has a naturally acidic pH in the range from 4-6, probably averaging 4.7. This acidic nature of skin is called the acid mantle and is vital for the proper functioning of skin. The low pH helps to protect the skin from bacterial infection, protects the barrier function of skin and helps the skin enzymes function properly. If the pH varies greatly, skin problems arise which may include infection, dehydration, dermatitis, roughness, acne, irritation, and noticeable flaking.

For a refresher, the pH refers to the concentration of hydrogen ion. It is a logarithmic scale that goes from 1-14 with 7 being neutral, less than 7 acidic and higher than 7 alkaline (basic). The pH of a solution can be measured with a pH meter, pH of skin is more difficult to measure and requires more specialized equipment. Read more here.

 What can affect the skin's pH?

The most common thing that we do that can change the pH of the skin is cleansing the face with soap or other cleansers that have a high pH. Healthy skin can come back to its normal pH after a few hours, but not all skin can tolerate that challenge. Face toners are often used after cleansing to restore the skin pH back to acidic. Toners should always have an acidic pH for that reason. I like to use herbaldistillates/hydrosols for a toner.  Modern face cleansers though are typically not soap and are buffered to be an acidic pH. Soap however has a basic pH of about 10 which cannot be changed, that may work great on most of your body, but if you have problems with skin on the face, do not use soap there. You can find a good face cleanser here that is pH balanced to skin.

People have often asked me about cleaning their face with baking soda. This is a big no no because baking soda has a high pH between 9-10 (similar to soap) and is sure to disrupt the pH balance of skin due to its alkalinity. Even plain tap water can affect skin pH. Theoretically, tap water should be pH 7, but it is typically closer to pH 8 because of impurities.

Age also affects skin pH, increasing as we age. For this reason it is important that products for mature skin have a pH from 4-5. Skin moisture, sweat, sebum, anatomic site, and genetic predisposition also affect skin pH.

The skin's pH is maintained by secretions from the glands of the skin; both eccrine and sebaceous secretions.

Understanding the anatomy and function of skin can help you be a better formulator. If you would like to learn more, download our ebook “The Nature of Skin.”

What Does Skin Do?

We see our skin everyday and we always read about it being the largest organ of the body, but what exactly does it do? It must do something if it is an organ. What is the role of skin? Here are seven important physiological roles for skin.

1. Regulation of Body Temperature (Thermoregulation). The skin helps the body maintain its desired temperature of 98.6F or 37C. It does this by dilating (opening or enlarging) blood vessels on the surface to release heat, or by constricting blood vessels to retain heat. A second way is by secreting sweat which evaporates on the skin's surface so that in evaporating it has a cooling effect. Finally, the hypodermis layer of the skin provides insulation to maintain heat. The hypodermis is the deepest layer of skin under the dermis and is composed mostly of fat .

2. Protection. The skin is physical barrier that prevents not only bacteria, viruses, and fungi from entering the body but also keeps most things from the environment or that you put on your skin from entering the body. Yes, you may have heard differently but the skin absorbs very little of what goes on it. This is often called the Skin Barrier Function and it provides a barrier between the inside of the body and the outside of the body. If the skin surface becomes compromised, however, due to abrasion, pathogens and toxin can enter the body more easily.

Besides preventing things from getting into the body, the skin also prevents water from leaving the body thus preventing dehydration. In situations like severe burns to the body, preventing excessive dehydration becomes a major, life threatening challenge.

3. Sensation. The skin is a sensory organ that we use to evaluate the outside environment. Receptors in the skin transmit information on temperature, pain and pressure.  In some cases this can be very enjoyable, even sexual.

4. Excretion. Through the process of sweating the skin can secrete products of metabolism from the body as well as drugs and toxins. The skin also contains enzymes that process toxins helping to break them down.

5. Immunity. Cells of the immune system called Langerhans cells can be found in the skin ready to be called into action when necessary to prevent infection. The skin also participates in the inflammatory response to protect the rest of the body from potential pathogens.

6. Blood Reservoir. Approximately 8-10% of the total blood volume of the body resides in the skin. When necessary this blood can be sent to the skeletal muscles to increase oxygen and nutrients there when needed it is directed to the more central parts of the body to maintain warmth.

7. Endocrine gland.  The skin acts as an endocrine gland by making hormone vitamin D or more specifically vitamin D₃ from 7-dehydrocholesterol (7-DHC), a process that requires sunlight or UVB radiation. This vitamin D3 is then sent to the liver for additional processing. Vitamin D is important for the absorption of calcium from the intestines as well as other less defined roles.

Want to learn more about skin physiology? You can purchase our downloadable class notes here.