COMEDOGENICITY: An ingredient or product causes the formation of comedones (blackheads) in a relatively short period of time.
Blackheads form when the outer layers of our skin do not shed properly and the hair follicle is blocked. The blackhead part comes from the oxidation of fatty acids on the surface in the skin. Scienticians still aren't really sure what causes this lack of desquamation (love that word!). Formation of comedones are not accompanied by skin redness.
ACNEGENICITY: An ingredient or product has the potential to cause or aggravate acne.
Acne forms when the skin doesn't shed and sebum accumulates in the follicle and sebaceous glad. This allows anaerobic bacteria to proliferate. The duct expands until it ruptures, and the bacteria makes it to our skin, causing an immune reaction and inflammation. The irritation may come from the fatty acids the bacteria have digested in our skin and are now spreading on our skin. Formation of pustules are generally accompanied by skin redness.
PUSTULOGENCITY: An ingredient or product has the ability to cause inflammatory papules and pustules in a short period of time. This tends to be dose dependent - a little might be fine, a lot might be trouble. You can get pustules with non-comedogenic ingredients (like SLS) due to irritation.
SENSITIVE SKIN: An ingredient or product has the ability to cause some people to react adversely. It can be a feeling that one cannot tolerate the product - for instance, sensations of burning, itching, stinging, and a feeling of tightness - or it can include redness or swelling. Sensitive skin can include allergic contact dermatitis and photoallergic reactions. The most common form is sensory irritation.
Most of these reactions are dose dependent. A small amount might be just fine, whereas a large dose can result in even the hardiest skin showing a reaction.
Many breakouts and pimples we attribute to our products are not, in fact, from the products. A pustule does not develop overnight from using a product - it can take up to 7 days for the process to go from start to finish. If you try a product today and find a pimple in the morning, it is almost certainly not from the product!
Comedogenicity is generally tested on both animal (rabbits) and human subjects, and the results can be very different depending upon which test was conducted. For instance, IPM - one of the most comedogenic oils or emollients - shows a score of 1 (from 1 to 3) on rabbit ears, but 0.4 on human skin. Rabbit ears are more sensitive than human skin, so the scores tend to be higher from animal tests.
What factors can pre-dispose someone to one of these skin irritations? Between 2 and 8.3% of the population has some kind of reaction to cosmetic products.
- Women tend to be slightly more likely to have skin irritation from products.
- A hypersensitivity to sensory input can make slight sensations like stinging or burning even more severe.
- There's an inverse correlation between age and susceptibility - it goes down as we get older.
- People with fair skin are the most reactive; dark skin, the least reactive.
- Area of the body - people can be sensitive on the face, but not the arms, and so on.
People with diminished barrier function in the skin - for instance, people with pre-existing skin conditions - should always be careful when trying new products.
A chart for comedogenic ingredients...seems like a good one.
So what does this all mean? Although the charts for comedogenicity are a great guideline, oftentimes the only way to know how you're going to react to something is to try it. If you know you have sensitive skin, then keep a list of various ingredients that might be irritating to you and avoid them.
What if there's an ingredient you really want to try but are fairly sure might irritate your skin? Many studies have found that many vegetable oils have a high comedogenic potential that can be reduced by adding 25% mineral oil to the mix (which has quite a low comedogenicity score). And no, I'm not sure exactly why that might be...
Just thought I'd share this as we finish up daily mineral make-up posts (look for mineral make-up Wednesday to return on September 30th) and start in on lotion and emulsifiers!