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The pH of soap and what it can do to your skin!



  In this month's experiment we are going to investigate the pH of a variety of soaps to determine if the level can potentially cause an irritation to the skin. Our skin has what is called an "acid mantle" which is a coating over our skin which is a combination of skin oil and perspiration. This acid mantle protects you from the elements like wind, cold and water and also making it harder for bacteria and other microbes to grow. It is a slightly acidic cover with a pH of between 4.5 to 5.5 for most people.
 

However because of its pH level your “acid mantle” can be removed if soaps raise the pH of your skin to anywhere above 6. It has been found that soaps with a pH of anything higher than 8 has the potential to remove the acid mantle and extract lipids from your skin, which can result in that dry skin feeling you occasionally get after washing yourself.

So which soaps have the potential to remove your acid mantle?.

Equipment

1 x pH22 - Pocket pH-mV meter with +-0.01 pH accuracy
1 x Goats Milk Soap Bar
1 x Sandalwood Soap Bar
1 x Pumice Soap Bar
1 x Home brand Soap Bar
1 x Moisturising Cream Soap Bar
1 x Small Knife
200ml of Deionised Water
3 x Beakers for rinsing the pH22 

Figure 1: All of the equipment ready to undertake the measurements

Method
The pH22 was initially calibrated at pH4 and pH7 using the included buffer solutions and relevant calibration procedure detailed within the manual. Small pieces of soap were then cut off each of the soap bars and were placed into small containers. One by one each of the soap samples were tested using the pH22. The small pieces of soap were placed into the tip of the pH22 and a small amount of distilled water was added to ensure enough moisture was present to establish a reading. Readings were then recorded when the meter stabilised. Between each test the meter was thoroughly cleaned. The results can be viewed in the section below.


Figure 2: Soap and distilled water in the tip of the pH22 undergoing measurement

Results

Test

Goats Milk (pH)

Sandalwood (pH)

Pumice (pH)

Home Brand (pH)

Moisturising Cream (pH)

1

10.14

10.33

10.32

10.49

7.48

2

10.16

10.34

10.34

10.51

7.49

3

10.16

10.34

10.32

10.51

7.49

Average

10.15

10.34

10.33

10.50

7.49

 
Table 1: Shows the relevant pH readings for each of the types of soap tested.

Discussion
The results show that out of each of the soaps tested 4 of the 6 were high in alkalinity. These included the “Goats Milk”, “Sandalwood”, “Pumice” and “Home Brand” soaps. Whilst they will certainly get you clean, these 4 soaps would certainly have the potential to break down your “acid mantle” and would in some cases leave you with that dry, tight skin feeling. Once the “acid mantle” is broken up it can take hours or it to restore itself and during this time your skin can feel quite dry.

The “Moisturising Cream soap” would be the most suitable soap choice out of the soaps tested as its pH of 7.49  is only slightly higher than your skin’s natural pH so it can still break down dirt and oil effectively without drying out your skin.

If you would like to discuss this experiment further please contact one of our friendly Scientists via email or phone on 1300 737 871.
  

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