The scientific definition of this value is: “The pH value is the negative decadic logarithm of the hydrogen ion concentration” and thus a measure of the acid concentration in aqueous solutions. The pH value thus indicates how acidic or alkaline a solution is. The pH value scale ranges from 0 to 14.
Acids have a pH value less than 7 and bases have one greater than 7. The average value of pH 7 is called neutral. You can measure pH with indicator solutions, indicator papers or with a pH meter.
Examples of different pH values (rounded).
- 1 – gastric juice, battery acid
- 2 – Lemon juice
- 3 – vinegar
- 4 – Cola, sauerkraut
- 5 – Skin, mineral water
- 6 – Milk
- 7 – distilled water, blood
- 8 – intestinal juice
- 9 – soap
- 11 – Detergent, ammonia
Importance for the skin
The skin can also be assigned a ph value, because the hydrolipid film on the surface of the skin contains water. Already a hundred years ago, it was known that the skin is slightly acidic. With modern measurement methods, it was possible to determine that the average ph value of the skin is between 5.4 and 5.9.
How does this value come about?
Horny scales, sebum, sweat and microparticles together form an acidic environment. This is also known as the protective acid mantle of the skin. This protective mantle helps to ward off harmful microorganisms as well as negative environmental influences, thus protecting the skin from infections, irritations, allergies and dehydration.
Every time the skin is cleaned with soap, this protective mantle is lost and the physiological balance of the skin is disturbed. The ph-value of the skin is raised to about 9 for a short time. However, healthy skin manages to lower the value back to normal within 30 to 200 minutes.
