Medea's Sunscreen is a brand of sunscreen used by demigods. It is presumably only for magical uses. It's only named variant is SPF 50,000. In the myths, Medea, the sorceress, gave this to Jason, though it wasn't known as "sunscreen" then (it was called magical lotion).
When SPF 50,000 is used, it makes the user invulnerable to some types of fire.