How to use period underwear for the first time: the whole routine, step by step

Step by step

1. 1

   Pick the tier before the style

   Choose the absorbency first, in millilitres, not by the word on the label. The same word covers different capacities at different brands, so turn your flow into a covering tier first, then choose the cut you like inside it.

2. 2

   Check the size on that brand's own chart

   Sizing is not consistent between brands, and period underwear is usually final sale. Measure around the fullest part of your hips and read that brand's chart, not your usual size in another label.

3. 3

   Put them on like any underwear

   Nothing is inserted, positioned or stuck down. The absorbent panel is already sewn into the gusset, so a pair goes on and sits like ordinary underwear.

4. 4

   Wear them for as long as your flow allows

   Saalt says how long depends on your flow and the absorbency level of the style you chose. Thinx says to change pairs at least every 12 hours to help prevent leaks. Expect fewer hours on a heavy day than a light one.

5. 5

   Learn the signs it is time to change

   A gusset that feels damp instead of dry, a panel that feels heavier and clings closer, and last of all a leak at an edge. Check by touch on a heavy day rather than waiting for the leak.

6. 6

   Rinse cold as soon as you can

   Knix says to rinse under cold water until the water runs clear. Modibodi says to rinse straight after use and until the water runs clear. Cold is the part that matters, because heat sets blood into the fabric.

7. 7

   Wash cold after every wear

   Knix says to machine wash cold with mild detergent, and to wash after each wear rather than getting a second day out of a pair. Saalt's wash page and Modibodi both say to skip fabric softener. Saalt's wash page and Thinx both say no bleach.

8. 8

   Air dry

   Saalt's wash page says no tumble dry, because high heat damages elastics and the leakproof gusset. Modibodi says to hang or line dry. Knix says to lay flat to dry. No brand instruction we read puts a pair in a tumble dryer.

9. 9

   Rotate the pairs, and replace when absorbency fades

   Run enough pairs that a clean one is always in the drawer. Modibodi says its garments last up to 100 washes with its care instructions. Replace a pair when it starts leaking earlier than it used to at the same flow.

Before the first wear: tier first, then size

Two decisions happen before the pair ever arrives, and they are the two that decide whether the first wear goes well. Tier comes first. Every brand publishes a capacity claim per tier and the words do not line up across brands, so the label alone will not tell you what you are buying. Our absorbency table normalizes every claim to millilitres with a grade for how it was sourced, and the translator turns a description of your flow into the covering tier at each brand. Pick the number, then pick whichever cut you like inside it.

Size comes second, off that brand's own chart. Period underwear is usually sold final sale for hygiene reasons, so a size guess is not free the way it is with ordinary underwear. One hip measurement is enough: the size finder returns your size at every charted brand, computed in your browser.

The first wear itself

Nothing goes in and nothing needs positioning. The absorbent panel is sewn into the gusset, so a pair goes on like ordinary underwear and stays where underwear stays. Most people wear nothing else with them. Saalt names both patterns on its own page: worn on their own, or as a backup to a cup or on a light day, where it says you may be able to wear a pair all day. A familiar pad on top for the first cycle is a common bridge while trust builds.

Wear a clean pair at home once before the day you actually need it. That tells you whether the cut sits right and what the panel feels like dry, which is the baseline you will be comparing against later.

How long a pair stays on, and how you know

The brands answer this differently, and every answer is about the product rather than about you. Thinx says its newest styles carry all-day leakproof absorbency for period protection up to 12 hours, and tells wearers to change pairs at least every 12 hours to help prevent leaks. Saalt says how long you can wear a pair depends on your flow and the absorbency level of the style you chose, that on a heavier day you may need a fresh pair after a few hours, and that on a light day or as backup you may get all day. Neither is a rule about a body, because hours are capacity divided by flow rate. The hours guide does that arithmetic.

The signs are physical rather than numerical. The gusset feels damp instead of dry. The panel feels heavier and sits closer. A leak at an edge means you are already past it. On a light day a morning-to-evening wear rarely reaches any of the three.

The routine, in order

The same nine steps at a glance:

• Pick the tier in millilitres, then the cut.
• Check the size on that brand's own chart.
• Put them on like any underwear. Nothing to insert.
• Wear for as long as your flow and that tier allow.
• Change when the gusset feels damp, before the leak.
• Rinse cold until the water runs clear.
• Machine wash cold after every wear. No fabric softener, no bleach.
• Air dry. No tumble dryer.
• Rotate several pairs, and replace one when it leaks earlier than it used to.

What happens after you take them off

This is the part people picture as the hard part, and it is a rinse. Knix, Thinx, Saalt and Modibodi each publish their own care instructions, quoted in the steps above, and all four say a version of the same four things: rinse cold until the water runs clear, machine wash cold, nothing that coats or bleaches, no heat. The wash guide covers that routine in full, including why each step matters and the two habits that shorten a pair's life fastest.

Away from home there is rarely a sink in the moment, so a small zippered wet bag holds a used pair until there is one, and the away-from-home guide has that version.

Rotation is the last habit, and the one that makes the routine invisible. Modibodi says its garments last up to 100 washes with its care instructions. Enough pairs that a clean one is always in the drawer means no laundry day becomes urgent. The lifespan guide covers the signs a pair is finally done.

Sources

The facts above trace to:

• Up to 12 hours of wear, changing at least every 12 hours, machine washing cold before first wear and after each use, no bleach, ironing or dry cleaning, and hanging to dry: Thinx, "How They Work." Read 2026-09-05.
• Rinsing under cold water until it runs clear, machine washing cold with mild detergent, laying flat to dry, no bleach, no fabric softener, and washing after every wear rather than getting a second day: Knix, "How to Wash Period Underwear." Read 2026-09-05.
• Wear time depending on flow and absorbency level, a fresh pair after a few hours on a heavier day, all-day wear as backup or on a light day, and sweat and discharge among the uses for the Regular and Light styles: Saalt, "Learn About the Saalt Period Underwear." Read 2026-09-05.
• Rinsing in cold water until it runs clear, a cold delicate machine cycle in a delicates bag, a gentle fragrance-free detergent, no fabric softener, no bleach, no tumble dry because high heat damages elastics and the leakproof gusset, and line drying: Saalt, "How to Wash Period Underwear." Read 2026-09-05.
• Rinsing straight after use until the water runs clear, a gentle cold machine wash, a laundry bag, no fabric softeners or strong detergents, line drying, and up to 100 washes: Modibodi, "How to best care for your Modibodi underwear." Read 2026-09-05.
• Brand tiers in millilitres, graded for how each claim was sourced: our own absorbency table and the live catalog, computed 2026-09-05. Each capacity is that brand's own claim.