How much jewelry should a hairdresser wear?

Ideally, minimal.

Rings with "bits" poking out and bracelets can get tangled in the hair of your client.

Long necklaces can also get tangled in long hair, unless the necklace is securely kept beneath clothing.

Elastic bracelets with no dangly bits or chains attached might be okay if they are tight against your writs. A lot of hairdressers wear elastic hair ties around their wrists in case they need to use them.

Piercings are not an issue for hairdressers.