I forgot what site I got this from, but it is very good information. If you know exactly where it came from, please PM me, and I'll edit it to give proper credit. *** I have come to learn that this was posted by tangal on EDS. But I believe the original is from Diana Yvonne Skin Care Board ***.
The initials pH stand for "Power of Hydrogen" or "Potential of Hydrogen." Both terms are correct. This is a measure of the hydrogen ion content in a solution.
The pH scale measures how acidic or alkaline a product is, compared to pure distilled water (which is pH 7.0). Only wet substances have a measurable pH. The skin's pH is actually the pH on the skins surface from the moisture within the skin, and the "acid mantle" which is part of the protective "barrier" on its surface. Hair for example has no pH.
The acid mantle is a fine film layer, slightly acidic, made up from skin oils, sweat, and dead cells. It is one means the skin uses to protect itself from bacteria, moisture loss, and environmental damage. Pollutants, harmful bacterium, contaminants are normally alkaline in nature, so a slightly acid skin surface helps fight off these harmful elements and prevent them from entering into, and damaging the skin. Maintaining the acid mantle is recommended for good skin health. When the acid mantle is damaged it takes approximately 14-17 hours to repair itself (assuming no other damaging products are applied to it).
A damaged acid mantle leads to a number of skin issues, such as over dry skin, dehydration, over oily skin, flaky skin, acne, sensitivity, etc. It would require another long post to detail all this. But incorrect pH products can contribute to acid mantle degradation, and increases in acne-causing bacteria on the skin. (More on this below)
The pH Scale
The pH scale goes from 0-14. This covers most wet substances, and certainly all skincare products.
-Acids have pH values under 7 - they are more acidic then water (acid)
-Alkalis have pH values over 7 - they are more alkaline then water (base)
-If a substance has a pH value of 7 - it is neutral, like water (neither acid nor base)
The difference between each whole-value pH level represents a tenfold change. (For example, a cleanser with a pH of 6 is ten times more alkaline than a cleanser with a pH of 5, and a cleanser with a pH of 7 is 100 times more alkaline then one of 5.) Because of this, only a few units of pH can make a big difference in how your skin reacts to a product.
Some pH examples:
pH 1 = Battery acid
pH 1.5 -2 = gastric (stomach) acid
pH 2 = lemon juice
pH 2.5 = cola soft drinks
pH 3 = vinegar
ph 3.5 = orange juice
pH 4.6-5.5 = healthy skin (and recommended pH range for your cleanser, for best skin health)
pH 5.5 = rainwater (pure water, when exposed to the atmosphere, will take in carbon dioxide, changing its pH)
pH 6.5 = milk
pH 6.5 â€“ 7.4 = healthy saliva
pH 7 = pure distilled water - (This is neutral pH, neither acid nor base)
pH 7.35 â€“ 7.45 = human blood
pH 8.5 = baking soda (damaging to skin's acid mantle)
pH 9 = seawater
pH 9.0-10.0 = hand soap, detergents (very damaging to acid mantle)
pH 10.5 = Milk of Magnesia
pH 11.5 = household ammonia
pH 12.5 = household bleach
pH 13 = lye (sodium hydroxide, or Draino)(Alkaline or Base extreme)
Skin and the Acid Mantle
Newborn baby skin has a neutral pH of 7. Within a few months it adjusts to a more "normal" pH of 4.5 to 5.5, enabling it to be more resistant to bacteria.
Adult skin is normally slightly acidic, a range of 4.5 to 5.5. Different body areas can differ in pH, and disease and acid mantle damage can alter pH. But the preferred range for facial skin pH is 4.5 to 5.5.
Those with skin disease, skin problems, and stressed skin usually have a skin pH over 6.0. Aged, stressed and damaged skin have more difficulty maintaining a â€œcorrectâ€ pH.
As skin pH is elevated closer to pH 7.0, it becomes less and less able to function optimally and to kill bacteria. This allows acne-causing bacteria to multiply rapidly on the skin's surface. (Acne bacteria are found on everyoneâ€s skin, even if you never have a pimple in your life.) The damaged skin is unable to fend off the excess bacteria, and they multiply rapidly. Bacteria growth is very slow at pH of 5.5 or less, but a slight shift upward, toward the alkaline levels, causes a marked increase in the reproduction and lifespan of acne-causing bacteria.
So if your skin is at a higher pH (anything over 6, as damaged skin often is) the acne-causing bacteria can multiply much easier and faster -- often faster then your skin can handle. Skin pH is one main contributor to acne.
Skin pH also has an effect on how easily irritated your skin is, how well it ages, and how it deals with product and environmental stress. This is why it is recommended that you cleanse skin with mild, non-irritating products, as close to the skin's natural pH as possible.
Many commercial cleansers are highly alkaline, which also changes the skin's pH to alkaline levels on the skin surface, for a short time. Many alkaline cleansers are in the same pH range as baking soda, and some are nearly as high as ammonia. This is very harsh on the skin, and can lead to increased irritation, acne, moisture loss, skin aging etc. As pimples erupt, the skin is less able to heal itself, or the damage that pimples leave behind.
If a product has a high pH and a considerable percentage of a strong detergent such as sodium lauryl sulfate, or irritant like peppermint oil or menthol, because of the pH destructive activity on the acid mantle, the detergent can contribute to even more damage then it would if the product pH was closer to 5.5. It literally takes a split second for an alkaline product to degrade the skin barrier enough for an irritant or damaging detergent to penetrate. Some people can handle this better then others, but long term daily use on the skin can contribute to long term issues on all skin types. As skin ages, or the barrier function degrades, it has more difficultly dealing with this type of stress.
Even when the skin re-adjusts to its more normal pH (4.5 to 5.5) - it is already damaged, irritated and stressed. The damage recovery involves longer term healing; 14 to 17 hours for acid mantle repair. Continued long-term damage, stress, and mild irritation can prevent the skin from maintaining its best pH level of 4.5 to 5.5. With time, and increased damage, it may tend to stay at the 6 range or higher.
As skin become healthier, its pH values lower, and acne growth also lowers. The skin becomes more "normal" and regulated.
Listing of pH of many common cleansers:
The pH of Common Cleanser
A few examples from above link:
Burt's Bees Tomato, Carrot, and Lettuce soaps 10
Dial Soap (liquid and bar) 9.5
Dove Bar, Baby Dove Bar 7
Johnson & Johnson Head to Toe Baby Wash 6.5-7.0
Neutrogena Facial Cleansing Bar Original Formula 8.7-9.2
Paula's Choice (all formulations) 5.5
A product may include the term "pH Balanced" on the label. This does NOT mean that it has an optimal pH of 5.5. The term has no legal definition.
Some products are a good pH, but high in irritants. Which is better then high pH and high irritants, but not great either.
A good cleanser cleans the skin without breaking down the acid mantle, or adding irritants to the skin. It is mild with a 5.5 or lower pH.