In the circle of life, we will often see some people with allergic skin, which is caused by the use of cosmetics. So what ingredients in cosmetics can cause skin allergy?
Type I allergens: preservatives
There seems to be no clear logic as to which substance is more likely to cause allergy, but some do seem to have a tendency. Usually, allergies are caused by preservatives. The two most common allergens are p-hydroxybenzoates and methyl isothiazolinone / methyl chloroisothiazolinone, which are widely used.
Type II allergens: fatty acids
Fatty acids also affect people to some extent. The most common fatty acid is stearic acid, but myristic, palmitic and oleic acids can also cause allergic reactions. It's strange, because these things are very common in food, and there's no literature that says people are allergic to them when they eat them. This type of allergic reaction is also highly related to the formula itself, so it becomes more difficult to find out the cause.
The third type of allergens: essence and essential oil.
Essential oils and essential oils are very typical allergens. The EU has established regulations requiring that 26 common allergens (if any) be listed separately when using these products. This is a very pragmatic move because flavors and essential oils contain many ingredients.