How do you know when a wound reached the dermis?

What do you mean?: The epidermis is so thin (think "roof" of a blister) that nearly all wounds reach the dermis. The dermis is the thick, sturdy portion of the skin (think the tough, fuzzy part of leather) and the epidermis is the waterproof layer on top (think the smooth layer on top that gives the leather its "finish"). Even a scratch often reaches the dermis. Hope this helps, but if not, ask again!