Acne appears when a pore in our skin clogs. This clog begins with dead skin cells. Normally, dead skin cells rise to surface of the pore, and the body sheds the cells. When the body starts to make lots of sebum (see-bum), oil that keeps our skin from drying out, the dead skin cells can stick together inside the pore. Instead of rising to the surface, the cells become trapped inside the pore.

What's Going On: If it's big, red, and painful, you're probably experiencing cystic acne, one of the more severe types. "Cystic pimples are caused by genetics and hormonal stimulation of oil glands," says Zeichner. Not only are they large, but they're also notoriously tough to treat. They often recur in the same place, because even if you manage to get rid of one, it can keep filling up with oil again and again, like an immortal pimple.
For UVA protection, a sunscreen with a high UVA protection of PA+++ or higher of PA++++ as recommended, especially to treat PIE. PPD is the UVA equivalent of SPF; use a sunscreen with a minimum of PPD20. The PA+ system has a + that corresponds to a tier of PPD protection. Of note, different countries use different PA systems. Japan and Taiwan changed their PA system to a 4+ tier system while Korea uses a 3+ tier system.

Acne treatment that you apply to the skin: Most acne treatments are applied to the skin. Your dermatologist may call this topical treatment. There are many topical acne treatments. Some topicals help kill the bacteria. Others work on reducing the oil. The topical medicine may contain a retinoid, prescription-strength benzoyl peroxide, antibiotic, or even salicylic acid. Your dermatologist will determine what you need.