Favus (Lat., 'a honeycomb'), a disease of the skin, chiefly of the hairy scalp, characterised by yellowish dry incrustations of more or less roundish form, and often cup-shaped, composed of the Sporules and Mycelia (q.v.) of a vegetable growth belonging to the order of Fungi (q.v.), with usually an unpleasant mousy odour. The discs of favus are produced with great rapidity, and spread rapidly, if not attended to at the first, over the whole scalp, destroying the bulbs of the hair, which becomes very short and thin, and then falls out altogether. Favus is a disgusting and unsightly, but hardly a dangerous disorder; it is, beyond doubt, contagious, but only spreads where cleanliness is greatly neglected, and is therefore almost unknown among the better classes. It is far more common among children than among adults, often affecting those in delicate health, and seems to be more frequent in Scotland than in England, and more frequent also on the Continent than in either England or Scotland. It seems to be gradually diminishing in frequency. On the general surface of the body it is easily cured; but on the hairy scalp its eradication is a matter of great difficulty. The treatment consists in careful removal of the crusts and scrupulous cleanliness, pulling out the hairs from affected parts by the roots, and the persevering employment of ointments containing a parasiticide. Resorcin, a substance allied to benzoic acid, is much praised by recent writers. General tonic treatment is usually necessary. Favus, if allowed to run its course unchecked, is almost always followed by permanent baldness of the parts affected; unlike Ringworm (q.v.), which is a minor disease of the same order.
The Favus fungus, Achorion Schænelinii, is nearly allied to the fungus which is so destructive to vines, and has by some botanists been placed in the same genus, Oidium.