COAL TAR

Several products containing coal tar are licensed for dandruff, seborrhoeic dermatitis and psoriasis of the scalp. Some also contain other constituents (see below).

Coal tar’s mode of action is unclear; it does not appear to reduce cell proliferation, but apparently prevents dandruff forming by interfering with the formation of intracellular cement. It also appears to impede the formation of sebum and to have antipruritic properties.

Presentations include shampoos, an ointment and a cutaneous emulsion.
Concerns have arisen over possible carcinogenicity and mutagenicity of coal tar, and special precautions for handling the raw material are now required, but so far no restrictions have been placed on the use of manufactured products.

SALICYLIC ACID AND SULPHUR

Salicylic acid promotes shedding of keratinised epithelial cells. It is included in one anti-dandruff shampoo and in combination with coal tar in the ointment mentioned above.

A minimum 1 per cent concentration is reported to be necessary to show a keratolytic effect on the scalp, but a prolonged contact time is needed and the effect takes up to 10 days to develop.

The only salicylic acid shampoo contains 0.5 per cent, is greatly diluted on application, contact time is minimal, and not enough is likely to be left on the scalp after rinsing to exert a residual effect.

The ointment contains 2 per cent and is likely to be more effective.

Sulphur is believed to increase sloughing of cells via an inflammatory process. It is included in the ointment.

ANTIMICROBIAL DETERGENTS: CETRIMIDE, UNDECENOIC ACID, BENZALKONIUM CHLORIDE

Cetrimide, a quaternary ammonium antiseptic and cationic surfactant, together with antifungal agent undecenoic acid, is included in one shampoo. Benzalkonium chloride 0.5 per cent is the sole constituent of another.