Comedogenic

What Does Comedogenic Mean?

Comedogenic describes a substance's tendency to cause comedones — blocked hair follicles that manifest as blackheads (open comedones) or whiteheads (closed comedones). A comedone forms when excess sebum, dead skin cells, and sometimes bacteria plug a follicular opening. Ingredients rated as comedogenic accelerate this process, making them problematic for acne-prone and congestion-prone skin types.

The Comedogenicity Scale

Cosmetic chemists use a 0–5 scale derived from rabbit ear assay studies: 0 = will not clog pores; 1 = very low likelihood; 2 = low; 3 = moderate; 4 = fairly high; 5 = high. Generally, ingredients rated 0–2 are considered safe for acne-prone skin, while 3–5 are typically avoided in acne-conscious formulations.

Limitations of the Scale

The original scale was developed using rabbit ear skin, which is significantly more sensitive and follicle-dense than human facial skin. Many dermatologists and cosmetic scientists argue the scale has limited predictive validity for human skin responses. Concentration matters enormously — an ingredient rated 3 used at 0.5% in a formulation may cause no issues, while another at 10% might. Individual variability is also significant.

Practical Guidance

Rather than fixating on individual ingredient ratings, patch test new products, introduce them one at a time, and monitor skin response over 4–6 weeks. Look for labels stating "non-comedogenic" — while not regulated, they indicate the brand tested the full formulation, which is more relevant than any single ingredient's rating.

See Acne Solutions for full product guidance.