In general, if the thing or things being altered are not permanent features, such as minor makeup or hair malfunctions, you can safely have these retouched without worrying about any significant impact to the “authenticity” of your headshot. If you have a temporary case of acne or blemishes without any “scar” damage that changes the surface of the skin, and it is truly just a temporary condition and not permanent or chronic, then it is okay to retouch it to remove it. However, be really honest with yourself: if it is a common condition, headshots etiquette says it should stay in the photo.