Cyclopentasiloxane
A light silicone that evaporates after you apply it. It spreads other ingredients evenly, gives instant silkiness, then leaves without residue.
Curly Girl note: It evaporates rather than building up, but it is usually a carrier for non-soluble silicones — check what else is in the formula.
About Cyclopentasiloxane
Cyclopentasiloxane, often called D5, is a small ring-shaped silicone. Unlike dimethicone it is volatile: it evaporates from the hair over minutes to hours after application. That makes it an ideal carrier — it helps serums, heat protectants and shine sprays spread in a thin, even layer and gives an immediate silky, weightless feel.
Because it evaporates, cyclopentasiloxane on its own does not cause build-up. The catch is what it carries. Most formulas that use it also contain non-volatile silicones such as dimethicone or dimethiconol, which stay behind on the hair once the D5 has gone. That is why we mark it as caution for the Curly Girl Method rather than avoid: the ingredient itself is fine, but look at the rest of the list.
Who tends to like it: people who silk press or flat iron, who want a light serum that does not feel greasy, and people with fine hair who dislike heavy oils. People with low porosity hair often prefer evaporating silicones over heavier ones for the same reason.
There is also an environmental angle. The European Union restricted D5 in rinse-off cosmetics because it persists in the environment, and many brands have since replaced it. Cyclomethicone is a label name for a blend of these ring silicones and behaves the same way.
How our checker rates it
| Mode | Rating | Why |
|---|---|---|
| Curly Girl | Caution | Evaporating silicone — mostly evaporates, but strict CG followers avoid all non-soluble silicones. |
| Relaxed hair | Good | Silicone — coats the strand and helps protect relaxed hair from heat and friction. |
| Low porosity | OK | No concerns for this mode. |
| Protein-sensitive | OK | No concerns for this mode. |
Ratings assume it is listed near the top of the label. After the first preservative or fragrance (likely 1% or less) most cautions soften.
What evaporating silicone ingredients do
Light, volatile silicones that spread other ingredients and then mostly evaporate from the hair.
Also listed as
- d5
- decamethylcyclopentasiloxane
Similar ingredients
Sources
Last data update:
- Robbins CR. Chemical and Physical Behavior of Human Hair. 5th ed. Springer; 2012. Reference text on hair structure, surfactants, conditioning agents, protein, heat and chemical treatments.
- Massey L, Chiu M. Curly Girl: The Handbook. Workman Publishing; 2011. Origin of the Curly Girl Method rules (no sulfates, no non-soluble silicones, no drying alcohols).
- Cosmetic Ingredient Review (CIR). Ingredient safety assessments. Safety assessments for cosmetic ingredients cited on ingredient pages.
How we research and update pages: editorial policy. Spotted an error? Tell us.