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!

Hi, I have some further doubts about niacinamide and acids.

What if they’re combined in a single product? Does niacinamide reduce to niacin and become useless? I’m using something like this: Aqua(Water), Mandelic Acid(10%[?]), Lactobionic Acid, Niacinamide, Sodium Hyaluronate, Allantoin, Hydroxyethylcellulose, Polysorbate 20, Ethylhexylglycerin, Phenoxyethanol, Parfum(Fragrance), Butylphenyl Methylpropional, Hydroxycitronellal, Limonene, Linalool. I’m not flushing [maybe shizo].

Niacin isn’t useless, it just causes flushing for some people – that’s all.

The amount of niacinamide hydrolysis depends on the pH of the product, how long it’s been stored for, and at what temperature. It’s also possible that there isn’t much niacinamide in the product. Unless it states the amount on the package there’s no way to know, it could be 0.1% or 4%.

If you’re not experiencing flushing and enjoy using the product – then keep using it!

Hope that helps 🙂

In vivo study of comedone reformation

Using a microscopy technique researchers were able to “watch” what happened to a comedone a week after it was removed.

Previous research has shown that comedones have a cyclical nature, either forming into inflammatory acne, re-appearing, or resolving.

Based on clinical experience, this cycle was estimated to take between 2-6 weeks. However, no studies had been done that provided direct evidence for this timeline.

A week after the comedone was extracted the skin appeared to resolve – to the naked eye. Under a microscope, however, researchers found that dead skin cells and sebum were already beginning to accumulate and reform the comedone.

This highlights the importance of continuing acne treatment even after the skin looks like it has cleared. This may also provide evidence for the use of acne treatments over the entire face or affected area instead of spot treating.

Further research with this technique could show how acne treatments prevent this comedone reformation, if there is individual variation on this reformation, what changes in the skin cells is causing the excess build up, and how long a lesion needs to be treated before the pore returns to normal.

Study finds link between sleep times and sebum production of women’s skin

This paper found a correlation between the time that female subjects went to sleep and how much sebum their skin produced.

A slight increase in sebum production was seen the later they went to sleep. As well, sleeping less was correlated with a slight decrease in sebum production. This relationship wasn’t seen in the male participants of the study.

They also found a correlation between levels of free testosterone and 5α-reductase (an enzyme that converts testosterone in to dihydrotestosterone – a more active form).

Curiously this correlation was, again, only significant for women – despite men having 10 times more free testosterone than women. The researchers think that there may be a maximum threshold for how much testosterone can influence sebum production. There’s also research indicating that the sebaceous gland’s sensitivity to testosterone varies among individuals as well.

While the study’s sample size was quite small, and it’s completely possible this isn’t reproducible, due to random chance or some other variable…there is newer research describing a pathway between inflammation and sebum production – which may be what’s at play here.