Skin and Soap pH
I want to know if a soaps pH will affect your skin? If so
then would a high pH or low pH damage your skin? Then what pH of soap
would be best for normal skin? Oily? Dry? Combination? Sensitive?
Just covering the basics:
Neutral water is pH 7
Acid is pH lower than 7 (goes down to 0)
Alkaline is pH higher than 7 (goes up to 14) (also called "base" or "basic")
The CO2 in the atmosphere gradually makes exposed damp surfaces mildly acidic: pH ~ 5-6.
We're very well accustomed to that pH.
Alkaline stronger than pH 8, such as pH 10, is very irritating to the skin.
Harsh soaps which bother us tend to do it that way.
Concentration also matters. A pH 9 solution can be as dilute as 10 parts per million,
or as concentrated as salty sea water.
The concentrated one is usually harsher, it's effects last longer on your skin.
Harsh soap in water may be a dilute pH 9, but if not rinsed off well enough,
after the water dries it's more concentrated on your skin and might then cause pH 10 for a little while.
Of course strong acids will hurt your skin too.
But that's for pH's of 3 or lower. An acid needs to be pretty strong to bother skin.
Lemon juice has pH roughly 2.3. You could wet a spot on your arm with that, let it dry, and in a little while it will itch.
You should rinse your skin fairly well then, and again maybe half-hour later.
I think pH 5-8 is the OK range for skin. Or maybe even a little wider.
That's not very discriminating, but, sorry, I don't know so much about skin care.
I think neutral or slightly acidic products are usually mildest. pH 6-7, I guess.
Inside your body, the blood is about pH 7.4.
The exact best pH for the outside of your skin may be a bit different than that.
The exact best may vary from person to person, and from time to time.
Or a pH range of 2 (i.e., from 5.5 to 7.5) may simply not seem to matter to your skin.
Finding out from your own experience, for your own skin,
would be unusually good scientifically informed consumerism.
I think a given liquid hand-soap or lotion could have it's pH moved as far as +/- 1.0 pH units,
by addition of small amounts of acids or bases which are already mentioned in the ingredients list on the label.
Citric acid and Sodium citrate are reasonably safe for the job.
Bi-phosphates, NaH2PO4 for acid and Na2HPO4 for alkaline, are OK too.
I often see phosphates on the label.
I think it's OK to dissolve the acid or alkaline in a little pure water,
then mix into the lotion or soap just enough of this solution to cause the pH change you planned.
You'd need some narrow-range pH Paper to see what change you'd made.
It's not hard, but if you have not taken chemistry class,
then you would need the assistance and perspective of someone older who has,
and the supervision of an adult.
Largely to make sure that the chemical is what you think it is, and not something stronger.
Web-surfing might turn up some stuff about specific pH effects on skin.
Sorry I haven't had time to try it for you.
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Update: June 2012