Dear Mr. Ko, Could you offer your professional opinion of comedogenic scales

like those used by CosDNA? Have these been discredited, or is there something to them? I see lots of people attempting to single out and eliminate specific acne “triggers” — i.e. specific troubling ingredients — and I’m wondering if so doing is a fool’s errand? What do you think?


CosDNA doesn’t list their sources (to my knowledge), but comedogenicity data is generally performed on rabbits, or rabbit ears specifically.

A high % (50% to 100%) of the ingredient is placed on the ear for a period of time and then monitored for comedones. Sometimes the ingredient is injected under the skin.

Researchers started coming to conclusions that moved them away from using these 1 ingredient animal results.

Firstly, while rabbit ears easily form comedones, they don’t correlate to human skin.

And secondly, using 1 ingredient in a high concentration doesn’t reflect its use in a consumer product.

Human sebum, for example, is very comedogenic. But it doesn’t cause problems for everyone.

My personal opinion is that the melting point of an oil or wax is more indicative of whether it will cause clogs or not. If your skin is warm enough to melt it, it’ll remain in a more fluid state, and less likely to clog pores.

It gets more complicated when you consider irritancy of an ingredient as well. While an ingredient might not be pore clogging, if it can cause enough irritation it may cause already formed microcomedones or comedones to erupt into inflammatory acne. This sometimes gets characterized as “purging”, especially common with prescription retinoids and chemical peels.

Hope that helps!