Soap and pH - Recovery time

Yesterday we learned that between the pH range of 4-9, hair really does not show any surface or internal changes. Now we focus on the surface and chemical changes that may occur.

Note: Hair is known to have a slightly acidic pH but there is great variance among individuals. Scientific studies have reported values as low as 3 and others as high as 6.6.

Q1: After using soap, does the pH of hair change?

The most likely answer is yes. I could not find an answer directly about hair but I did find one on skin. Even washing with water produces a change in pH, however soap does produce the most change (Dermatology pp258-262, 1997)

Wash Product
Product pH
pH change to skin
Tap water 7.9 +0.198
Synthetic detergent 1 5.5 +0.294
Synthetic detergent 2 5.5 +0.291
Soap 9.5 +0.453

Q2: How long does it take skin/hair to 'recover' from alkaline pH

Anywhere from 45 minutes to 3 hours (British Journal of Dermatology, Volume 76, Issue 3, pp 122-125, 1949)

Q3: Does pH affect anything else (hint: bacteria and fungi)

Yes washing regularly and repeatedly with soap is thought to disrupt the normal flora of the skin. (In case you didn't know, we are crawling with bacteria and this is normal). Disruption of this bacteria can lead some to proliferate more than others (Acta Derm Venereol.;67(1):41-7, 1987). Please do note that this has to be regular and repeated (for example twice a day, every day).

Q4: Are castile soap or baking soda with an alkaline pH irritating?

Let me start by saying the normal test to look for sensitive skin is to use SLS, a superb surfactant. Regardless of pH, (which it can be made to pH 4-7) it can be very irritating. Do remember irritance comes from removal of the oil layer causing dryness and itchiness. 

There is however a strong relationship between pH and irritancy. Generally between ph 4 and 9, there isn't much irritation (meaning it may still be there but will not be disturbing). Outside this range, irritation can increase markedly (International Journal of Dermatology, pp494–499, 2002)

Depending on the pH of your baking soda mix or castile soap dilution, you may experience irritation.

I will save the juicy questions for last - Tune in tommorow for Q&A: Should you really use castile soap and or baking soda ( including silicone removal and whether pH is sufficient to relax hair).


  1. So is the effect of castile or any other type of soap the same for my scalp and the skin on the rest of my body?

  2. Sorry for the late response Nina - The effect should be similar but there may be slight differences. The scalp has a barrier - hair - while skin has much less hair in comparison.

  3. What can I add to Dr Wood's Tea Tree Castile Soap so that it will have a pH of 4 (haven't used it yet, purchasing online now)? I think the pH of my skin might be too high and causing my underarms to have a strong smell. My underarms smell soon after bathing with no deodorant around 45 minutes after. By the way, deodorant with aluminum only works maybe 3 hours. I am attempting to use more natural products so I stopped using Dial Antibacterial Soap (with triclosan) after using it for about 10-15 years.

    Also would aluminum free baking soda and water mixed together make an effective deodorant? Any suggestions on what to add to make it better? I am a 21 year old woman. Please help :( I am embarrassed in public and even around my family because of my smell.

    1. after you bathe at night, dry your body and underarms, then rub your underarms with fresh lime or lemon (just cut off a small wedge so you can use the whole lemon for a while) and let air dry. It will kill the bacteria that eats the sebum produced by your underarms causing the smell. In the morning, bathe again (or simply just re-wash your underarms really well with soap), dry your underarms and rub with lemon again. Continue this process every morning and night until you notice the smell is gone. Then you can try skipping the night time application. I haven't worn deodorant or antiperspirant for years now and suffered a good year with the smell before creating this regimen. In the beginning you will notice the smell decreasing daily. It doesn't sting like you think it would, even after shaving. Good luck! I know its a bit of a late response but I hope it helps you or any other reader!

    2. Lime or lemon? Interesting :)

    3. Lemon is what I used since I was a kid. But I guess lime will work as well


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