The antimicrobial activity of dyes was first reported in 1913.
Azo dyes (eg, scarlet red and phenazopyridine HCl) are most active in an acidic medium and are effective against gram-negative organisms. Scarlet red has been used for decades as a 5% ointment/dressing on sores, ulcers, wounds, and skin grafts. Fine-mesh gauze impregnated with a preparation of scarlet red blended with lanolin, white petrolatum, and olive oil can be used as a dressing for donor skin graft sites or burns. Note that azo dye products should not be used on cats, because they are particularly toxic to this species, on account of cats' deficiencies in glucuronide conjugation.
Acridine dyes (eg, acriflavine, proflavine, aminacrine) are more active against gram-positive bacteria. Their activity is enhanced in alkaline medium and antagonized by hypochlorites. Bandages, gauze, and acriflavine jelly impregnated with acridine dyes have been used extensively to treat burns. Acriflavine causes frameshift mutations and has been used to attenuate various veterinary pathogens for the development of live vaccines.