Amodimethicone is an amino-functional silicone: a polydimethylsiloxane (PDMS) chain carrying grafted aminoalkyl groups. At the acidic pH of conditioners and masks, these amine groups become protonated and give the silicone a positive charge, which draws it towards the negatively charged sites of keratin. Bis-Aminopropyl Dimethicone belongs to the same family but carries its aminopropyl groups at both ends of the chain. These amino silicones deposit preferentially where the hair is most damaged, which sets them clearly apart from conventional dimethicone.
For hairdressers the difference is practical: a neutral silicone deposits evenly everywhere, while an amino silicone targets lengths and ends sensitised by bleaching, colouring or heat. Hairswiss explains the mechanism behind this selective deposition.
What is an amino-functional silicone?
The backbone is the same as that of dimethicone: alternating silicon and oxygen atoms (–Si–O–) carrying methyl groups. This chain is highly flexible, has low surface tension and is hydrophobic, which explains the slip and shine that all silicones provide.
In amodimethicone, some of the methyl groups are replaced by amine-bearing side chains, usually of the aminoethylaminopropyl type, which carry a primary and a secondary amine. These groups are spread along the chain like hooks. Bis-Aminopropyl Dimethicone is built differently: the PDMS chain is linear and carries a single aminopropyl group at each end.
In both cases the share of amine groups stays low compared with the siloxane backbone. The silicone keeps its hydrophobic character but gains an anchoring function.
Why do amino silicones bind to hair?
Keratin has an isoelectric point close to pH 3.7. Above that value the hair surface carries a net negative charge, due to the carboxylate groups of acidic amino acids. Oxidative treatments strongly increase this charge: during bleaching, part of the cystine disulfide bonds is oxidised to cysteic acid, whose sulfonate group (–SO3⁻) stays ionised even at acidic pH.
The amines of amodimethicone are protonated at the pH of care products (usually between 4 and 5.5) and become ammonium groups (–NH3⁺). An electrostatic attraction then forms between the silicone and the anionic sites of the fibre. The more oxidised an area is, the more negative charges it carries and the more silicone it attracts: this is the principle of selective deposition.
This mechanism brings amino silicones close to the cationic surfactants used in conditioners, such as Cetrimonium Chloride or Behentrimonium Chloride, with which they are almost always formulated.
How does amodimethicone differ from Bis-Aminopropyl Dimethicone?
- Amodimethicone: pendant amine groups spread along the chain. The polymer anchors at several points and forms a fairly covering film. It is often supplied as a microemulsion with non-ionic emulsifiers (for example Trideceth types), which makes it easier to disperse in masks.
- Bis-Aminopropyl Dimethicone: terminal amine groups only. The chain anchors by both ends, while the central part stays free and faces outwards. The resulting film is thin and very slippery, and mainly provides smoothing and frizz control.
In both cases deposition tends to be self-limiting: once the silicone has neutralised the anionic sites, the surface becomes less attractive to further cationic molecules. This lowers the risk of build-up compared with a heavy dimethicone, which deposits through hydrophobic affinity alone.
What measurable effects do they have on hair?
On bleached hair, the surface has lost much of its 18-MEA lipid layer and has become hydrophilic. Amino silicones rebuild a hydrophobic film on these areas. Effects observed in the lab and in the salon include:
- lower combing forces, measured wet and dry with instrumental tests;
- a more hydrophobic surface, which limits fibre swelling in humidity and therefore frizz;
- greater shine, linked to the optical smoothing of the cuticle;
- better colour retention, as the film slows the diffusion of dyes out of the fibre during washing.
These silicones do not repair keratin: they compensate at the surface for part of the lost properties. Combined with hydrolysed proteins, they complete a treatment that also works in depth.
Do amino silicones build up?
Their affinity for the fibre makes them more resistant to rinsing than a neutral silicone or a volatile silicone such as cyclomethicone. Thanks to self-limiting deposition, however, build-up stays moderate with a normal routine. On fine or very frequently treated hair, a more cleansing shampoo every two to three weeks is enough to reset the surface. Before colouring or bleaching, a prior wash ensures even uptake of the product.
Which professional treatments contain amino silicones?
Liss Komplex Hydra Mask by Edelstein, available on cliCHair.ch, uses Bis-Aminopropyl Dimethicone as its key active, combined with Cetrimonium Chloride, a cationic esterquat, and hydrolysed keratin and silk. This combination illustrates the thin, smoothing film approach described above, suited to frizz-prone hair.
Swiss professionals also find on cliCHair.ch the Nika Age Restore Deep Conditioner, which bases its detangling effect on amodimethicone combined with Behentrimonium Chloride and Stearamidopropyl Dimethylamine, an amidoamine activated by the lactic acid in the formula.
How can you recognise them in an INCI list?
- Amodimethicone: the most widespread amino silicone, often followed by Trideceth-10, Trideceth-12 or Cetrimonium Chloride, signs of the microemulsion.
- Bis-Aminopropyl Dimethicone: amino silicone with terminal groups.
- Trimethylsilylamodimethicone and Aminopropyl Dimethicone: variants of the same family.
- Not to be confused with PEG/PPG Dimethicone, silicones made water-soluble by polyether chains, with no amine groups and no electrostatic affinity.
Conclusion
Amodimethicone and Bis-Aminopropyl Dimethicone are “smart” silicones in the chemical sense: their protonated amine groups steer them towards areas of oxidised keratin, where the hair needs them most, and their deposition limits itself once the charges are neutralised. For hairdressers they are the tool of choice for bleached, coloured or heat-damaged hair, provided they are paired with suitable periodic cleansing.