Modern patches are made from a hydrocolloid material – a gel‑forming blend of pectin, gelatin and carboxymethylcellulose – that is sealed to a thin, flexible, waterproof outer layer. When placed on a raised pimple, the hydrocolloid draws fluid such as pus, oil and dead skin cells into its gel matrix, causing the patch to turn white or cloudy.

At the same time, the patch forms a physical barrier. It covers the blemish, making it harder to pick, squeeze or touch, which reduces the chance of new bacteria entering and worsening inflammation.

Some brands add active ingredients like salicylic acid, tea tree oil, niacinamide or benzoyl peroxide. These actives help exfoliate the skin, calm redness, or target the acne‑causing bacteria, giving the patch an extra therapeutic boost.

The patches work best on pimples that already show a white or yellow head, because the pus is close to the surface and can be absorbed by the gel. For optimal results, apply to clean, dry skin, leave on for six to eight hours or overnight, and replace it once it becomes cloudy and swollen.

In short, hydrocolloid patches treat pimples by sucking out fluid, shielding the spot from further irritation, and, when medicated, delivering acne‑fighting ingredients directly where they are needed.