How bite and scratch protection work
Every piece of clothing has a bite value and a scratch value, and each one only counts on the body parts that item covers. A T-shirt does nothing for your forearms, and a helmet does nothing for your neck.
Values from several items on the same body part are added together (one source). The Protection tab of the health window lists the total for each part. Bullet defense is a separate third value that matters only against firearms.
A blocked attack can still tear a hole in fabric, and a holed part loses its protection until you repair it. On default settings a bite that reaches skin always infects, while scratches and lacerations infect only some of the time, so bite protection is worth more than scratch protection. One Build 42 guide names the head, neck, torso and forearms as the priority parts (one source).
Build 42 also added separate armor slots for the shoulders, forearms, elbows, thighs, knees, shins, groin and neck. These are worn over normal clothes.
