Is Polyester Activewear Bad for Skin?

The short answer

Yes, for many people. Polyester is a synthetic, plastic-based fiber that is hydrophobic (water-repelling). While it is marketed as "moisture-wicking," it primarily moves liquid sweat across its surface rather than absorbing it. This creates a "greenhouse effect" against your skin—trapping heat, bacteria, and sebum—which can lead to "Gym Acne" (folliculitis), irritation, and the proliferation of odor-causing bacteria.

1. The "Greenhouse Effect" and Pore Occlusion

Unlike Merino wool, which is hygroscopic and absorbs moisture while it is still in the vapor phase, polyester only starts "working" once you are already wet with liquid sweat. This delay causes pore occlusion, where a seal of sweat and plastic-fiber heat creates the perfect environment for Cutibacterium acnes to thrive.

2. Why Bacteria Love Plastic

Research shows that bacteria adhere more strongly to polyester than to natural fibers. Because polyester fibers are essentially smooth plastic tubes, they trap skin oils (lipids) that bacteria feed on. This is why synthetic gear often develops a "permastink"—the bacteria are literally anchored to the fiber.

3. The "Low-Tox" Skin-Friendly Alternative

Estroni uses 17.5–18.5 micron superfine Merino which is clinically proven to be non-irritating and therapeutic for sensitive skin barriers. By maintaining a stable "microclimate" between your skin and the fabric, it prevents the bacterial spikes that lead to skin irritation during and after movement.