[theBCnut]

Medicated shampoos can expire depending on what they are medicated with, but you shouldn’t have to worry about anything else.

If the shampoos are supposed to have some therapeutic properties, they may not work if mixed, but regular shampoos shouldn’t be an issue. I wouldn’t mix medicated shampoos. Some have iodine, sulfur or other ingredients in them that you need to be careful what they are mixed with or they could burn the skin.