Learn Italian: Ti sei fatta mettere lo smalto dall'estetista? - Did you have your nails painted by the beautician?

The verb fare normally uses avere in the past tense (hai fatto). However, when you use it in the reflexive causative construction (farsi mettere, meaning "to get something put on yourself"), the reflexive pronoun ti forces the auxiliary verb to switch to essere.

Why does fatta end in -a?

Because this sentence uses the auxiliary verb essere (Ti sei), the past participle must agree with the subject's gender and number. The -a ending on fatta shows that the person being spoken to ("you") is female. If speaking to a male, it would be Ti sei fatto mettere.

Why is mettere left in the infinitive?

In Italian causative constructions, the conjugated verb (fare) is always followed directly by an infinitive verb (here, mettere). You only conjugate the first verb. Literally, it's like saying "Did you make yourself to put the nail polish...".

Why does the sentence use mettere to mean "painted"?

In Italian, you don't usually use the literal verb for "to paint" (dipingere) when talking about nails. Smalto means "nail polish," and Italian uses mettere (to put) for applying most cosmetics. You are literally saying "to put on nail polish."