How important is pH in cosmetic formulas? 

1. Cosmetic formulas should match the pH of the skin or hair (most of the time)

The skin and scalp is slightly acidic – sitting around a pH of 5 – 5.5 – which is why many cosmetic formulas are pH adjusted to be within this very range. Where you can formulate serums, creams and lotions to a pH of 5 – 5.5, it is ideal to be compatible with the skin and scalp. Wash off formulas, such as cleansers for the face and body, can be a slightly higher pH, around 6 – 6.5, since they have a short contact time before being washed off.

The eyes, or more correctly the tears, have a pH of around 7. This means products that are formulated specifically for use around the eyes are best to have a pH of around 6.5 – 7 to avoid tearing or redness. Face creams shouldn’t have direct contact with the eyes; but anti-eyebag creams or serums for use around the eye area specifically should have a pH of around 6.5 – 7 to avoid potential irritation.

The hair is more acidic – around 4.5 – 5. Conditioners are typically formulated to a pH of 4 – 4.5 so that their key functional ingredients ‘cling’ to the hair, making it feel silky, soft, and easy to detangle. While this pH is a bit lower than the scalp, the short contact time does not pose any issues. Even leave on conditioning treatments, with longer contact times before rinsing off, don’t normally pose an issue since the product is applied to the hair rather than the scalp. Shampoo formulas commonly have a pH around 5.5 – 6 or 6 – 6.5, without an issue, because of the short contact time before rinsing off. Watch how to make a conditioner here, and how to make a tear-free shampoo here.

Finally, the pH of the mouth is around 7, which is considered neutral. Personal care formulas for use in the mouth, such as toothpaste and mouthwash, are usually formulated to be around 6.5 – 7 for this reason. Watch how to create an organic herbal toothpaste here.

2. Cosmetic ingredients that should be selected to suit the pH of the skin or hair

There are a lot of ingredients that go into various types of cosmetic formulas; these should be selected with the pH of the skin or hair in mind where possible. For example, any formula with more than 5% water present will need a preservative to be used. The preservative system selected will need to suit other ingredients in the cosmetic formula but should also suit the final pH that is needed to suit the skin or hair.

For example, there are a lot of cosmetic preservatives that fit a more natural cosmetic formulation philosophy. A lot of these preservatives suit a pH of 5.5 or less, so could be used in many types of skincare formulas. However, they won’t work in a shampoo formula, for example, where certain foaming ingredients require a pH of 6 or more to be stable. While that higher pH is fine for a shampoo formula, and may suit the foaming ingredients more, the preservative then needs to be changed to one that will be effective at a higher pH range. As another example, a preservative that needs a pH of 5.5 or less to be effective will be totally useless in a toothpaste where the pH should be 7.

Fortunately, a lot of cosmetic ingredients are ideally suited to a pH of around 5.5. This makes cosmetic ingredient selection easy for most types of formulas in many instances. Even where a slightly higher pH of 5.7 up to 6.5 is required for certain ingredients, such as polymers, to be used in a leave on cream formula, this normally doesn’t pose an issue to the skin and is still considered compatible.

3. Cosmetic ingredients that need to be formulated to a certain pH

There are times where we need to create cosmetic formulas to a pH that is not skin compatible to get the required activity from the cosmetic ingredient. Here are some examples:

• Zinc oxide will always stay around a pH of 7.0. No matter how much acid or alkaline you add to a formula containing zinc oxide, it will always move – typically within a day – back to around 7.0. This means all other ingredients selected for use in a formula containing zinc oxide must have a pH range of compatibility from 6 – 8, to suit the zinc oxide whilst allowing for a little bit of pH drift around that neutral value.
• DHA for tanning will always drop pH quite rapidly. DHA used in tanning formulas is one of the most incompatible ingredients you can work with as a cosmetic formula, so besides making sure your tanning formula lands at a final pH of around 5.5 – 6, you also need to formulate a tanning product to allow for that pH to become acidic, yet remain stable, over a relatively short period of time, without using any ingredients that it is incompatible with. Learn how to create a self-tanning lotion here.
• AHAs and BHAs – in fact, most acids – need to be in a formula at a relatively low pH, around 3.5, to be effective. Increasing the pH of these formulas to meet regulatory requirements will often render them useless; so you will need to check the cosmetic regulations where you want to use these ingredients and see if a formula makes sense. There are also usually strict limits on the input of these ingredients, so they can be tricky to formulate with, and comply with the cosmetic regulations in many regions. Read more about formulating with acids here.
• Oxidative hair dyes and depilatory agents require a very alkaline pH to be effective. All ingredients in these types of cosmetic formulas will need to be compatible with a pH of 11 or 12 respectively in order to maintain the stability of the cosmetic formula and ensure it will work as expected. These can be quite demanding formulas to create and ensure a long shelf life, as well as the required performance.

You can learn how to formulate sunscreens, tanning, whitening and acid formulas in both our Certificate in Advanced Cosmetic Science and Diploma of Personal Care Formulation; whilst the demands of creating formulas for oxidative hair dyes, hair perming and straightening agents and depilatory agents require you to study our Diploma of Personal Care Formulation.

4. If you are new to the pH of cosmetic formulation…

Don’t panic, creating cosmetic formulas to the right pH is not as scary as it sounds, and you can start formulating cosmetics using pH strips. Once you are formulating cosmetics more regularly, you should invest in a good pH meter, like you see us use in our videos. You can google to find suppliers of pH strips and meters depending on where you are at with your cosmetic formulation studies.

In the meantime, here are some other pH topics that will help you understand pH in cosmetic formulas better:

• Watch how to measure pH in cosmetic formulas – using pH strips and a pH meter
• How to prepare pH buffer solutions – this video has loads of beginner formulating tips including basic equipment. At around 17 minutes you will see how to make pH buffer solutions.
• Some basics about pH in cosmetic formulas – read here.
• Should cosmetics be diluted to test pH? The answer is almost always no. Read why in this blog.

And of course if you are very new to formulating and want a range of tips to help get you started right, please register for our FREE cosmetic formulation fundamentals masterclass which takes you through the basics of how to read formulas, understand pH, clean equipment and how to make a variety of skin and hair care formulas.

Happy formulating!