Wash your hands and ask before you pick up the baby.
No matter how irresistible that baby is or how recently you washed your hands before your arrival, just lather up again when you get to their house. Also, remember that the baby may have literally lived inside your friend body just days before and they're probably still feeling a bit possessive. Be respectful and ask if you can hold the baby. If after a few minutes your friend is looking uncomfortable and itchy to get baby back, pass baby back immediately.