Comfort

Skin and friction

Chafing has causes, and they are mechanical. Two surfaces, movement, moisture and time. Change any one of the four and the problem usually goes.

Friction damage to skin follows a predictable pattern. Two surfaces move against each other repeatedly. Moisture softens the outer layer of skin, which reduces its resistance to abrasion. Heat increases both moisture and blood flow. Given enough repetitions the surface is disrupted, which shows first as redness and heat, then as soreness, then as broken skin.

Every remedy works by removing one of those inputs: separating the surfaces, reducing movement, managing the moisture, or shortening the exposure. That is a more useful framework than a list of products, because it makes it obvious why a given fix works in one situation and not in another.

Where it happens

Under the band: Usually caused by a band that is moving. A loose band slides up and down against skin all day; a firm one sits still and does not abrade. Counterintuitively, a tighter band is often the fix for a band that chafes.
Under the wire: A wire sitting on tissue rather than behind it, or a wire end that has worn through its channel. The first is a fit problem covered on band and cup; the second means the garment is finished.
At the strap: Straps carrying load they should not be carrying, usually because the band is too loose. A wider strap spreads pressure but does not address the cause.
Between the thighs: Skin against skin, the hardest case because there is no garment edge to change. A short, meaning a brief with an actual leg, puts fabric between the surfaces and solves it outright.
At a leg or waist edge: A folded elastic edge under tension. A bonded or laser cut edge removes the ridge entirely. See shapes.

A band that chafes is usually a band that is moving. The instinct to loosen it makes it worse.

Fabric choices that help

Flat, bonded or covered seams rather than raised overlocked ones, particularly anywhere that will be sat on or lain on.
A fibre that takes moisture into itself rather than leaving it on the surface: cotton, modal or lyocell. See cotton and modal.
Smooth surfaces at the points of contact. Fine lace against a moving surface is an abrasive, however soft it feels in the hand.
Fewer layers of elastic in one place. Two elastic edges crossing at the same point on the body is a reliable source of a mark.
Correct size. A garment that is too small increases pressure and a garment that is too large increases movement, and both produce friction by different routes.

Sensitive skin

Where skin reacts readily, the usual culprits are fragrance, dye and detergent residue rather than the fibre itself. Fragrance is the most common contact sensitiser in laundry products and in anything applied to skin. Detergent left in a fabric because of an inadequate rinse is the second.

Wash new garments before wearing them, to remove finishing chemicals and loose dye.
Use a mild, fragrance free liquid detergent at about half the recommended dose.
Add a second rinse for anything worn against skin for long periods.
Skip fabric softener entirely. It leaves a coating that some skin objects to and reduces the absorbency of the fibres underneath.
Where a specific garment is the trigger, wear it alone for a day to confirm before replacing an entire drawer.

The same reasoning applies to what is put directly on skin. Fragrance free is the safer default, and washes formulated for intimate skin, such as those stocked by inWonderstate, are built around exactly that principle rather than around scent.

Managing an existing sore patch

Keep the area clean and dry, remove the source of the friction, and give it air. A soft bralette with no wire and a wide soft band gives skin under the bust a chance to recover; a short does the same between the thighs. Avoid reintroducing the garment that caused it until the skin has settled fully, because partially healed skin abrades far faster than intact skin.

When it is not friction

A mark that appears without an obvious mechanical cause, a rash that spreads beyond the contact area, skin that does not settle within a few days of removing the cause, or anything painful, weeping or spreading is not a fitting question. That belongs with a doctor or a pharmacist, who can look at it. Nothing on this site substitutes for that, and a persistent skin problem is worth taking seriously early rather than experimenting with for weeks.