What is it?
Stinging larvae that come from ocean animals such as jellyfish and coral; can get trapped inside a bathing suit.
What to look for
An itchy rash of tiny red bumps often under the bathing-suit line (usually not on exposed skin); also known as seabather's eruption.
What to do
Apply hydrocortisone cream or calamine lotion; rash usually fades within a week. For severe cases, see your doctor, who can prescribe a stronger anti-itch medication.
How to prevent it
Watch for beach postings of an outbreak. Have your child change out of her swimwear before showering, since fresh water can activate the stinging larvae.