Cyclomethicone

Also known as: Cyclopentasiloxane (D5), Cyclotetrasiloxane (D4), Cyclosilicone

Moderate ConcernsiliconeEWG: 5-7

A lightweight, evaporating silicone used as a carrier in hair products — but EU-restricted in wash-off products.

How it works

Cyclomethicone (particularly D4 and D5) is a cyclic silicone that evaporates from the skin, leaving behind a dry, silky feel. It is a popular carrier for other silicones and actives. However, evidence of environmental bioaccumulation and reproductive toxicity in animals led the EU to restrict D4 and D5 in rinse-off products at ≥0.1% from 2020.

Avoid if

EU rinse-off products (restricted)People prioritising environmental impact

Commonly found in

Hair serumsLeave-on conditionersAntiperspirants (D5)

Safety & restrictions

D4 (Cyclotetrasiloxane) is toxic to reproduction (Category 2) and a PBT substance. D5 is bioaccumulative and toxic to aquatic organisms. EU restricts both in wash-off products. Under review for leave-on restrictions.

Restricted / banned in:EU (wash-off products ≥0.1% — D4 and D5)

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For informational purposes only. Not medical advice. Consult a dermatologist for personalised guidance.