It's a non-toxic, synthetic modeling clay made from polymer polyvinyl chloride (PVC) base. Polymer clay is soft and pliable until it is cured.
Polymer clay is durable but should still be handled with care.
To clean, use a soft wet cloth, I like hand soap. To remove make-up, use a Q-tip with alcohol. To prevent damage, keep earrings stored in a safe place, ideally a small box.