Quick answer
Most everyday underwear should be washed after wear, but not every piece belongs in the same cycle. Separate delicate lace, molded or bonded pieces from durable cotton basics and let the care label control machine washing, temperature and drying.
Sort by construction, not just by category
Cotton briefs, synthetic performance underwear and delicate lingerie can have different heat and agitation limits. Elastane and elastic trims are especially worth protecting from unnecessary heat.
Machine wash only when the label allows it
For machine-washable underwear, choose a cycle compatible with the most delicate item in the load. A mesh bag can reduce snagging for some pieces, but it does not override a hand-wash-only label.
Detergent and rinsing
Use the detergent amount directed for the load and washer. More detergent is not automatically more hygienic; excess can leave residue when rinsing is incomplete.
Drying
Air drying is a conservative option for elastic-rich and delicate pieces. If tumble drying is permitted, use only the heat level allowed by the garment label and avoid unnecessary overdrying.
Item construction, filling, coatings, electrical components and trim can change the safe method. Follow the finished-item care label and manufacturer instructions when they are more specific.
Decision points for this item
wear frequency
Wash everyday underwear after wear unless the product label or special-use instructions say otherwise.
Close-to-skin garments accumulate body soils and perspiration.
Watch for: Do not use frequency guidance as permission to exceed the garment care label.
machine wash
Use a care-label-compatible gentle or normal cycle based on the item construction and fabric.
Construction and trims vary widely within the underwear category.
Watch for: A mesh bag reduces snagging but does not make a hand-wash-only item machine washable.
temperature
Use a cool or warm setting within the label limit; protect elastane, elastic and delicate finishes from unnecessary heat.
Fiber and elastic components determine heat tolerance.
Watch for: Do not apply one hot-water hygiene rule to every underwear fabric.
drying
Air dry or use only the tumble-dry heat permitted by the label; avoid overdrying elastic-rich pieces.
Drying risk is often driven by elastic, bonding and trim rather than the category name.
Watch for: High heat can shorten the useful life of elastic and delicate components.