What to know about skin sensitisation

Live in your best skin – what to know if you’re experiencing skin sensitisation.

Skin sensitisation is what happens to your skin when you have an allergic response to a substance after it comes into contact with the skin. Skin sensitisation may take the form of a rash, itchiness, bumps, peeling skin and breakouts to name a few. 

There are many materials, synthetic and natural, that should never be used in products that come into contact with your skin – for example, volatile compounds such as alcohol, fragrances and essential oils and non-volatile synthetic compounds such as glycols, surfactants and fatty alcohols along with natural fats and waxes to name a few.

Unfortunately, I see these materials too often in skin products that simply should not be there. They are in fact exacerbating the problem consumers are trying to solve. 

I’ve observed the scientific progression of skin sensitisation spanning my 30-year career in the cosmetic industry. I don’t blame the industry for this.

Being a product development chemist we were developing products we thought would benefit people’s skin, while also making them desirable to the consumer in terms of odour, colour, consistency and skin feel.

But if we continue to develop and supply products with known sensitisers in them, we will end up sensitising the consumer, who will then be unable to use any of these products ever again.

The alternative is to develop products without the sensitisers. This would mean a completely different looking skincare regime/product. No smell/odour, no more creams/lotions, no more face cleansers or exfoliants. So, what to do?

We need to address this issue while still delivering a product that works. I think we need to be proactive not reactive. Synthetic surfactants will need to be used if we want exfoliants and facial cleansers to work and maybe an odour enhancer as well, as surfactants don’t smell very nice. Both of these products are wash off, so the impact of these potential sensitisers is minimised.

When we look at leave-on products such as moisturisers, creams in their many forms, serums, gels and toners, the sensitisers need to be eliminated.

Most formulas contain 95 per cent or more ingredients that don’t help the skin, but are there to make up the base of the product. This includes synthetic emulsifiers, fragrances/essential oils and petrochemical derivatives.

The other five per cent or less is the active ingredients such as vitamins, plant extracts, proteins and man-made actives.

Most actives are non-sensitising so it makes sense to create products with just the actives’ ingredients in them. This not only eliminates the sensitisers but it delivers actives undiluted and at a level that will help the skin. 

It’s very similar to the clean raw food movement where eating fresh wholesome foods are far better for you than processed foods. The skincare products of the future will be either water-based, or oil-based.

This means if you want vitamins A & E you will need an oil-based product as both of these are only oil soluble in their pure plant form. For vitamins C & B you will need a water-based product as both of these are only water soluble.

Products containing oil soluble actives such as pure rosehip oil, sweet almond oil and macadamia oil are very good for lipid dry skin, and creating a barrier over damaged broken skin. There are many brands on the market with these types of products.

Skincare that only delivers water soluble actives at 100 per cent is a very new concept, but it can be done. New brands such as Biologi are developing technologies that allows water soluble nutrients to be delivered to the skin in their pure form from the plant.

Skin sensitisation 101

Substances are classified as skin sensitisers if there is evidence in humans that the substance can lead to sensitisation by skin contact 1. Allergic contact dermatitis, is a common itchy red skin rash you get when you come into contact with a chemical.

There are also many natural sensitisers; the number one is essential oils. There are about 300 different essential oils available, only eight have no sensitisers.

Skin sensitisation develops in two phases: Phase 1 – comprises immunological priming of the exposed skin tissue with the acquisition of sensitisation. Phase 2 – after a second exposure to the same chemical an aggressive immune response might be elicited resulting in a local inflammatory reaction.

The mechanisms by which a chemical interacts with the immune system comprise a direct chemical-protein reaction or an indirect reaction after conversion of the chemical into protein-reactive molecules. Over 3700 substances have been identified as contact allergens.

Is there a difference between sensitive skin and sensitised skin?

Yes. A good example of sensitive skin is when the skin is exposed to low humidity, cold conditions and becomes dry and itchy due to the surrounding environment and these symptoms stop when the environment changes to warmer/humid conditions.

A good example of sensitised skin is when the skin is exposed regularly to a product such as a daily cream or perfume and no reaction occurs initially and then quite dramatically the skin shows signs of irritation in the form of a rash, itchiness, bumps, peeling skin and breakouts etc.

The subject stops use of the product and the irritation goes away. The subject then starts use of the same product or similar product and the irritation returns immediately.  

Ingredients to avoid


  • Petrochemical derivatives such as glycols, silicones, liquid waxes (paraffin) and surfactants.
  • Man-made chemicals such as fatty alcohols (cetyl alcohol, stearyl alcohol and stearic acid) and perfumes/fragrances.
  • Preservatives such as parabens, phenyl ethyl alcohol, benzyl alcohol etc.


  • Essential oils
  • Alcohol / ethanol and methanol

For more on essential oils and fragrances compounds visit ifraorg.org

1 reconstructed-human-epidermis.com/epics/sensitization

Ross Macdougald is a formulation chemist, owner of essential oil supplier Phytoverse, owner of Plant Extracts and founder of Biologi. 

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