There are three kinds of minor wounds: lacerations, abrasions, blisters. Each one needs a different sort of therapy, and the condition of every wound will tell you whether or not you should get appropriate medical treatment, instead of simple first aid.
Lacerations: A laceration is defined as being irregularly shaped injury that will often have ragged edges of skin about it. These will also frequently involve deep skin damage, in addition to bruising, these are best treated by a doctor with an emergency area.
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Abrasions: Abrasions are shallow, usually grazes where the top layer of skin has been eliminated, like those located using a skinned knee. They must be analyzed carefully to see whether that debris can be easily removed, otherwise, get medical care.
Blisters: A blister is the consequence of friction being applied to the top two layers of skin via continuous pressure. Remove skin from the outside, and apply a protective dressing for quick healing.
Infected minor wounds will exhibit some rather definite physical signals. There'll often be indications of discoloration, redness of the skin around it, tenderness, a light covering of skin that's very fragile and a definite odor coming from the wound.
If this occurs, you must get medical treatment as soon as possible. Rounds of antibiotics or even wound debridement may be required to have the infection under control, and recovery has begun.