Cool Acrid Herbs that Release the Exterior

Which two herbs are used together because they both vent rashes; for incomplete expression of rashes, or itchy rash due to wind-heat?

Niu Bang Zi and Chan Tui are both good for venting rashes. They appear together in the formula Xiao Feng San, alongside other herbs from the W.A.R.E. category that vent rash, such as Jing Jie and Fang Feng. Chan Tui is the skin of cicada, so it's good for the skin.

Source: Bensky, D. (2004). Chinese Herbal Medicine: Materia Medica. Seattle, WA: Eastland Press. p. 50 [Q341]