Using your hands to spread salve, wash, tar and other wares is perfectly fine.  But you'll get the best coverage from a brush with over 2,580 boars hairs.  (Okay, we don't know the exact number...)

Our wooden comb is dual-use with a large teeth side and finer teeth on the reverse side.  Use the larger teeth for the sides and underneath your beard, and the smaller teeth for your chin and areas with less hair!