Amodimethicone

What it is

Amodimethicone is a silicone — a polymer made from a chain of silicon and oxygen atoms — that additionally carries amino groups. Those amino groups are the decisive difference from simple silicones such as dimethicone: they are weakly positively charged and deposit preferentially where the hair surface is negatively charged, that is, on the damaged parts of the fibre.

This gives rise to the principle of action: the deposit is distributed unevenly and sits mainly where the surface is rough. The hair combs more easily and looks smoother and glossier. The substance does not penetrate the fibre to any appreciable extent and repairs nothing; it improves the behaviour of the surface for as long as it is present.

Why

• Molecular size is the main argument for the classification. Silicone polymers of this order of magnitude are essentially not taken up through intact skin; they stay on the surface. That largely removes the question of an effect inside the body.
• “Silicones suffocate the hair” is not a tenable statement. Hair is dead material and does not breathe. The legitimate question is a different one: whether a deposit builds up over time and whether it can be removed again with the shampoo in use.
• On build-up: amino-functional silicones are used precisely because they adhere. Whether that turns into a troublesome build-up depends on the use level, the frequency of application and washing habits, not on the substance alone. That is a question of the care result, not a safety question.
• Not transferable: the environmental and regulatory debate around cyclic siloxanes such as D4 and D5 concerns small, volatile molecules. Transferring it to polymeric silicones without a separate examination would be methodologically inadmissible and is not done here.
• Safety and efficacy stay separate. The classification concerns tolerability. The visible effect is a surface effect and lasts as long as the deposit is present — no claim about “repair” of the fibre is connected with it.

When the assessment differs

• Fine hair and frequent application: a deposit is more likely to be perceived as weighing the hair down. That concerns the result, not safety.
• Leave-on compared with rinse-off products: in a conditioner the contact time is short, in a leave-in the substance stays on the hair and possibly the scalp.
• Before chemical treatments: an existing silicone deposit can affect how evenly colour or reshaping products are taken up. That is a processing matter; the manufacturer's specifications and the assessment of the hair govern.
• Sensitive scalp: irritation is not the typical issue with this substance. If complaints occur, other constituents of the formulation are more likely candidates, such as fragrances or surfactants.
• Children: not assessed here.

Open questions

• Concentration in the actual product: not available. Amino-functional silicones are usually used at low levels, but that does not replace a figure.
• Composition of the raw material: amodimethicone is often supplied as an emulsion together with further constituents that carry their own INCI names. This assessment concerns the named substance, not the other constituents of the raw material.
• Environmental behaviour of polymeric silicones in treatment plants and water bodies: a technical debate is under way. It has not been evaluated here and is not assumed for this substance either.
• Interaction with chemical treatments: the statement above is a technical assessment drawn from practice, not an evaluation of data.

Related substances

Applies to: Silicones

• Dimethicone — Silicone, smoothing

Further substances from the same group for which a long-form assessment already exists.