Vitamin E in formulas: antioxidant versus pro-oxidant effect

What do antioxidants do in a cosmetic formula?

Antioxidants provide two functions in a personal care formulation:

• act as antioxidants on the skin to reduce free radical damage to skin cells; as is caused by environmental conditions (this aspect will not be covered here as we are focusing on the antioxidant protection of a formula in this blog).
• act as antioxidants to protect the stability of the formulation from free radical damage and possible rancidity (this will be discussed in detail here).

Some materials may be excellent antioxidants for the skin, but have no antioxidant effect in a formula. Examples of this are dl-alpha-tocopherol acetate and ascorbic acid – both are great on the skin but no protective benefits on the formula. There are also dozens of herbal extracts with great antioxidant benefits for the skin, but they provide absolutely no anti-oxidant protection for a formula.

Antioxidants are not preservatives

Antioxidants are not preservatives – they provide no anti-microbial activity in a formula at all. In fact, they actually add to the food source for many micro-organisms! However they do help prolong shelf life where there is a high oil content in the product. For example:

• massage oils or similar products where they contain a high content of vegetable and/or essential oils, should contain a high proportion of antioxidant. This will help protect the product against rancidity.
• products that contain only triglycerides, esters, silicones and/or mineral oils will not normally need antioxidant protection of the lipid content.
• essential oils can quickly lose their top notes and begin smelling ‘off’; an antioxidant should be added to a finished product containing essential oils at moderate to high proportions to help slow the loss of top and middle notes.
• ‘natural’ face and body creams which contain between 5 – 10% vegetable and/or essential oils (and sometimes more) should contain a moderate to high proportion of an antioxidant to help protect the product from rancidity.
• antioxidants may also be required to protect the actives in your formulation or the formulation itself (for example, sunscreens) - the active ingredient information sheet usually advises if additional antioxidants are required to prolong the activity of the finished product.

Can antioxidants cause oxidation? When do they cause a pro-oxidative effect?

Interestingly, too much antioxidant CAN cause a pro-oxidative effect in your formula, but it totally depends on how much you have used compared to how much oxidative protection is used in your formula. There are a few journal reports discussing the pro-oxidative effect, but please remember, it totally depends on the specific formula and ingredients you are working with. There is no ‘magic’ input of how much antioxidant will provide protection, and how much will cause pro-oxidation, that applies as a general rule over every formula. This means you need to check your formulas for oxidation, and pro-oxidation, as the exact amount of antioxidant that is ‘just right’ for your formula, depends on your individual formulas, and varies from formula to formula depending on exactly what you have present in there.

To test and prove this point, I made a natural cream containing 15%w/w rosehip oil – one of the most readily oxidisable oils – and added varying amounts of tocopherol to this formula -  then tested them under various heat conditions to see which input was the most stable. Watch this video here to see the results.  What you see might surprise you! It also guides you in how to select a suitable starting point for antioxidants in your formulations, but also how to test that it is not too much, or too little, to provide the right amount of protection.

What natural antioxidant ingredients can protect a formula?

Suitable natural antioxidant ingredients to protect a formula include:

• tocopherol (vitamin E):
  • comes as d-alpha tocopherol (naturally derived) or as mixed tocopherols (naturally derived). Check the INCI names and specifications carefully, as dl-alpha tocopherol sounds similar but is actually synthetic!
  • Mixed tocopherols provide the best antioxidant benefit; d-alpha tocopherol the next best benefit and dl-alpha tocopherol the next best benefit.
  • comes as various % concentrates.
  • low use would be 0.3%; moderate use would be 0.5%; high use would be 1-2% (raw material – NOT active content).
  • too much antioxidant can have a ‘pro-oxidative’ effect and can actually INCREASE the rate of oxidation and IRRITATE the skin – this is believed to happen because of irritant effect of increased oxidation on the skin.
  • tocopherol acetate has no antioxidant protective benefits in formulas – it only provides antioxidant benefits to the skin.
  • vitamin E is oil soluble and commonly used in a variety of personal care products.
  • products that are ‘hot filled’ (e.g. balms, which are poured off while still molten) will need a high % of tocopherol if they are composed of vegetable and/or essential oils – part of the tocopherol is ‘used up’ protecting the formula during the hot fill process so more is needed to ensure adequate amounts are present in the finished product after filling/the product has cooled.
• rosemary extract:
  • moderate use would be 0.1%; high use would be 0.2%.
  • you will need to make sure it is a high quality rosemary extract (NDM) to impart effective antioxidant protection.
  • usually available as an oil soluble form, it can be used in a variety of personal care products but does have a rosemary aroma and will often taint the finished product a pale yellow.

How do you add an antioxidant to a formula?

Antioxidants should be added to formulas <40°C, as they themselves get oxidized by heat – and you really need them there over the 2-3-year shelf life of a product rather than being partially or wholly used up during the manufacturing process. Where you are making a hot fill product (for example, a lipstick or a balm) you have no choice but to add them when the formula is hot, but you add them at the last stage once all other ingredients have been melted/combined – this then exposes them to a slightly lower heat for less time than other materials. You would also use more antioxidant to protect a hot fill product as some gets used up protecting the formula during the filling process.

In addition to the use of antioxidants, dark or opaque packaging can also help to reduce the rate of oxidation of a product by reducing exposure of the product to light sources.

We can’t give you a ‘standard’ input amount for each of the antioxidants because it depends on your formula. Where there is a high oxidative risk, use a higher input of antioxidant. Where there is a low oxidative risk, use a low input. Where there is no risk, you can still add antioxidant for label claims and to provide a skin protective benefit.

The only way you can check, and know for sure, how your chosen anti-oxidant and input will perform over the shelf-life of a product is to conduct ‘accelerated stability testing’ – storing the product at 35°C or 40°C for an extended period to see if off-notes or colour changes develop. If they do, not enough antioxidant has been added! If they don’t, the product is sufficiently protected.

Happy formulating!