Used externally, it is an antiseptic and disinfectant, and is used 5 to 10% in ointments in the treatment of chronic skin diseases such as psoriasis, hidradenitis suppurativa, and eczema of a sub-acute character.[citation needed] It is present in over-the-counter topical acne treatments at 2% or less concentration, and in prescription treatments at higher concentrations.[11] Weak, watery solutions of resorcinol (25 to 35 g/kg) are useful in allaying the itching in erythematous eczema.[citation needed] A 2% solution used as a spray has been used with marked effect in hay fever and in whooping cough.