Urea.

What it does

As a natural part of skin's own moisturizing factor, low concentrations act as a humectant that draws in and holds water, while higher concentrations also work as a keratolytic that loosens and sloughs thickened, rough skin.

Benefits

• Deeply hydrates dry, tight skin as a skin-identical humectant
• At higher strengths, smooths rough, scaly, or thickened skin (heels, elbows)
• Supports the skin barrier and is a workhorse for xerosis, eczema, and ichthyosis
• Boosts penetration of other ingredients layered with it

Side effects

• Higher concentrations can sting or irritate, especially on broken or sensitive skin
• Prolonged or repeated contact may cause irritation in some users

Who it's for

Very dry, rough, flaky, or thickened skin (low % to hydrate, high % to exfoliate)

Who should be careful

Use high-strength (keratolytic) urea cautiously on the face, genitals, or broken/cracked skin, where it is more likely to irritate or sting