Washing your beard may seem no different than washing your head in practice. Using shampoo that's designed for your head seems like the natural choice because it's what we have available to wash hair with.
The problem with this convienence is that most shampoos are specially formulated for washing away mass amounts of natural oils that are secreted by our scalp beneath the hair. Your face skin is much more sensitive than the skin on your head and produces far less of the natural oils that the scalp produces.
Using a typical head and scalp shampoo will overdry the skin on your face causing itchy, flaky skin and poor beard health. Instead, it's recommended to use a shampoo designed specifically for the beard
The health of your beard is closely associated with the health of the skin underneath your beard.
In this Derm Dude podcast snippet - Long time friend and associate, Dr Heather Woolery-Lloyd and I discuss beard growth myths and facts as well as how using the wrong shampoo on your face can damage the skin and create an unhealthy beard growth enviroment.