Is polyester underwear bad for you?

Yes. Polyester underwear traps heat and moisture in your most sensitive areas, creating conditions for bacterial and yeast infections. It doesn't absorb sweat, breeds bacteria at 5x the rate of cotton, and can cause irritation from chemical finishes. Gynaecologists consistently recommend cotton underwear, particularly for people prone to UTIs or yeast infections.

What is the healthiest fabric for underwear?

100% cotton is the healthiest all-round choice — breathable, absorbent, hypoallergenic, and recommended by most doctors. Tencel/lyocell is even better for moisture management. Silk is excellent for sensitive skin. The key principle: your underwear should absorb moisture and allow air circulation, which rules out all synthetic fabrics.

Is nylon bad for underwear?

Nylon is better than polyester for underwear (it absorbs slightly more moisture and is softer), but still significantly worse than natural fibres. It doesn't breathe well, can harbour bacteria, and traps heat. If your underwear contains nylon, look for styles with a cotton gusset — the cotton panel where the fabric contacts your most sensitive skin.

Best Fabrics for Underwear: What Should Actually Be Against Your Skin

Your underwear sits against the most sensitive, warmest, most moisture-prone areas of your body. All day. Every day. The fabric choice matters more here than anywhere else in your wardrobe — and yet most people have no idea what their underwear is actually made of.

Here's a clue: if you bought it from a fast fashion retailer, it's probably mostly synthetic. And that's a problem.

Why Underwear Fabric Matters

The groin area is warm, enclosed, and moisture-rich — the ideal environment for bacterial and fungal growth. The fabric you put there either helps manage that environment or makes it dramatically worse:

Breathable fabric allows airflow, reducing moisture buildup and keeping temperatures manageable
Absorbent fabric wicks sweat away from skin, preventing the damp conditions bacteria love
Non-breathable synthetic fabric seals in heat and moisture, creating a warm, humid microclimate that's essentially a bacterial and fungal incubator

Gynaecologists have been saying this for decades: wear cotton underwear. It's not old-fashioned advice. It's microbiology.

The Best Underwear Fabrics

1. Cotton

The medical standard. Here's why:

Absorbs moisture. Cotton soaks up sweat rather than letting it pool against skin.
Breathes. Air flows through the open fibre structure, helping regulate temperature.
Hypoallergenic. Cotton almost never causes contact reactions — critical for sensitive areas.
Washable at high temperatures. You can sanitise cotton underwear at 60°C without damaging it.
Affordable and widely available. 100% cotton underwear exists at every price point.

Look for: 100% cotton or 95% cotton / 5% elastane (the elastane adds stretch without compromising breathability). Organic cotton if you want to avoid pesticide residues.

2. Tencel / Lyocell

Tencel is arguably the best technical fabric for underwear:

Absorbs 50% more moisture than cotton
Smoother fibre surface — less chafing and friction
Naturally inhibits bacterial growth
Softer than cotton against skin
Biodegradable, no microplastics

Tencel underwear is more expensive than cotton but increasingly available from brands like Organic Basics, Boody, and others focused on intimate wear.

3. Silk

Silk underwear is the luxury option with genuine functional benefits:

Natural antimicrobial properties (sericin protein)
Temperature-regulating — cool in summer, warm in winter
Ultra-smooth — minimal friction in sensitive areas
Absorbs moisture without feeling damp

The trade-off is cost and care. Silk underwear needs gentle washing and won't survive a 60°C cycle. But for people with chronic irritation or skin conditions, the investment can be worth it.

4. Merino Wool

Superfine merino underwear is excellent for active use:

Best natural odour resistance — can go multiple days between washes
Temperature-regulating in all conditions
Moisture-wicking without feeling wet
Ideal for hiking, travel, and multi-day wear

Not for everyone (some people find any wool against intimate areas uncomfortable), but for active lifestyles and travel, merino underwear is a game-changer.

What to Avoid

Polyester

Polyester is the worst fabric for underwear:

Zero moisture absorption. Sweat sits on your skin, creating a warm, humid environment.
Bacterial breeding. Odour-causing bacteria proliferate at 5x the rate of cotton on polyester.
Heat trapping. No airflow means temperatures stay elevated — increasing infection risk.
Chemical concerns. Heat and moisture increase the migration of dyes and chemical finishes from fabric to skin — and your intimate areas are highly absorbent.

If your underwear says "polyester" anywhere on the label, reconsider.

Nylon

Nylon is slightly better than polyester (it absorbs marginally more moisture and is softer) but still fundamentally non-breathable. Most fashion underwear and lingerie uses nylon because it's cheap, stretchy, and allows for intricate designs. Function takes a back seat to aesthetics.

The cotton gusset compromise: Many nylon underwear styles include a cotton gusset — a cotton panel in the crotch area. This is better than all-nylon but not as good as all-cotton, since the surrounding nylon still traps heat around the edges.

Underwear Fabric Comparison

Fabric	Breathability	Moisture	Odour Control	Skin Safety	Price
Cotton	Good	Good	Good	Excellent	$
Tencel	Excellent	Best	Very good	Excellent	$$
Silk	Excellent	Very good	Very good	Excellent	$$$
Merino	Good	Very good	Best	Good	$$
Nylon	Poor	Poor	Poor	Fair	$
Polyester	Very poor	None	Terrible	Poor	$

The Simple Rule

Cotton for everyday. Tencel for an upgrade. Silk if you want the best. Merino for active use. Polyester and nylon for the bin.

Your most sensitive skin deserves the best fabric. Check the label.