The invention provides a hair treatment composition comprising one or more alkaloids derivable from plants of the Sophora genus (Sophora alkaloids), characterised in that at least 95% by weight of the total Sophora alkaloids present in the composition are tetracyclic quinolizidine alkaloids of the general structural formula (I): in which X is O or a lone pair. The invention also provides the use of the above composition for the treatment of the hair fibre, especially hair fibres which are damaged.