If I did something to myself, I can use a reflexive verb and then le/la + body part. Eg: Je me lave les mains. (I wash myself the hands --> I wash my hands). Similarly: Il se lave les mains (He washes his [own] hands.)
If the body part is the grammatical subject of a verb, it wants ton/ta/mon/ma/son/sa/votre/notre/leur &c before it. For instance: Tes/vos lèvres sont rouges = your lips are red. Sa bouche est ouverte = His/her mouth is open.