Our Everyday Collection is treated with HeiQ Skin Care™ — Swiss synbiotic technology that supports your skin’s microbiome through fabric-to-skin contact. Underwear that works like skincare. It’s a cosmetic treatment that promotes healthy skin appearance, not a medical product, it doesn’t diagnose, treat, or prevent disease. UNDERskin™ is embedded directly into the fabric during production, so it’s working from the very first wear. No creams, sprays, or steps required.

No change to handfeel, breathability, color, or fit, it feels exactly like the Everyday you already love. Non-irritant, human skin patch tested, and all ingredients INCI-listed.

Please check out our size guide above. We offer free exchanges on unworn items, so if the fit isn’t right you can swap for a different size hassle-free. Not feeling it at all? We accept returns within 30 days of purchase.

Yes. The Everyday Thong is Underdays’ best option for minimal panty lines under any outfit, including white, thin, or body-hugging fabrics.

The Everyday Collection is ultra-soft modal — perfect for daily wear under work clothes, jeans, and dresses, and light activity like walking or gentle yoga. The Workout Collection uses moisture-wicking performance fabric designed to handle sweat and movement. Same flattering shape, but for anything higher intensity — running, HIIT, hot yoga — the Workout Thong will keep you drier and more comfortable.

Our core colors such as Black and Sand are always available and restocked regularly. Fashion colors and seasonal drops are limited edition — once they sell out, they won’t be coming back. If you spot a color you love, we’d recommend grabbing it before it’s gone. Follow us on social or sign up to our mailing list to be the first to know when new color drops land.