ORGANIC 

Pertaining to carbon - based compounds produced by living plants, animals or by synthetic processes. Referring to substances that are or have been alive, and therefore contain carbon molecules in their chemical structure. 

OUTER ROOT SHEATH

A soft thin layer surrounding the lower two-thirds of a hair.

OVARIES

In women, a major source of female hormones. Certain conditions involving the ovaries can lead to excess hair growth, especially polycystic ovary syndrome (PCOS).

OVERTREATMENT

Overly aggressive treatment to remove hair which leads to temporary or permanent skin damage.

OXIDATION COLOUR 

A colour which requires oxygen to make it work.