Learn Italian: Lavo la pelle con acqua e sapone. - I wash my skin with water and soap.

In Italian, when you talk about body parts, you usually drop possessive words like mia (my) if it is obvious whose body it is. You just use the definite article (la).

Could I say mi lavo la pelle instead of lavo la pelle?

Yes! When washing your own body parts, Italians usually use the reflexive form (like mi lavo le mani for I wash my hands). However, lavo la pelle is also correct here. It focuses slightly more on the skin itself as the object you are cleaning, rather than emphasizing your daily personal hygiene routine.

Why are there no articles before acqua and sapone?

When you use a substance or material in a general way, especially after the preposition con (with), you often leave out the article. Con acqua e sapone acts as a set phrase, exactly like the English phrase with soap and water.

Both pelle and sapone end in -e. How do I know their genders?

Nouns ending in -e can be either masculine or feminine, so you have to memorize their gender when you learn the word. In this sentence, pelle is feminine (la pelle) and sapone is masculine (il sapone).