Why is my period underwear leaking? 5 causes and the fix for each

Start here: the 30-second diagnosis

Which one sounds like your leak?

• Leaks through the middle on a heavy day: the absorbency is too low for your flow (cause 1).
• Leaks at the leg edges or the pair feels loose: it is a fit problem (cause 2).
• Leaks after several hours: you are past its capacity, change sooner (cause 3).
• Leaks even on a light day, or wets through fast: the wicking is shot, usually fabric softener (cause 4).
• Leaks toward the back when sitting or sleeping: the rise is too low (cause 5).

Cause 1: the absorbency is too low for your flow

The most common leak. A pair rated for light or moderate flow cannot hold a heavy day, no matter how well it fits. The word on the label ("Heavy," "Overnight") is not a reliable guide, because it means different capacities at different brands. The fix is to match the pair to your actual flow in millilitres: put your flow into the absorbency translator and it shows the covering tier at each brand, then wear a pair that clears it on your heaviest hours (with a cup or tampon as backup on the very heaviest).

Cause 2: the fit at the legs

If the pair gaps at the leg openings or feels loose, blood escapes at the edges before the gusset can absorb it - the pair can be the "right size" on the label and still leak if it does not seal. Period underwear is sized on your hip, not your usual size, and brands disagree, so a size that fits in one brand can be wrong in the next. The fix is to get your real size for that brand from your hip measurement, and if you are between sizes, size up for a snug seal rather than down.

Cause 3: you have worn it past its capacity

Even the right pair leaks once it is full. If you get several good hours and then a leak, you have simply reached its capacity for your flow rate - it is doing its job, you just left it on too long. The fix is to change sooner, or move up to a higher-capacity pair so the change point lands later. On a heavy day that can mean changing every few hours, the same as you would a tampon.

Cause 4: the wicking is shot (usually fabric softener)

If a pair that used to work now wets through quickly or feels like it repels rather than absorbs, the absorbent layer is coated. Fabric softener is the usual culprit - it leaves a waxy film that stops the fabric taking up liquid - and detergent or hard-water buildup does the same. The fix is a strip wash (a hot soak with the right agent to pull the buildup out), and then never use fabric softener on it again. If a strip wash does not revive it and the pair is a couple of years or 40-plus washes old, it is simply worn out and due for replacement.

Cause 5: the rise is too low for how you leak

When you sit or lie down, flow runs backward, toward your tailbone. A low-rise pair leaves the absorbent panel short of where the flow actually goes, so you leak at the back even though the gusset is barely used. This is the classic overnight leak. The fix is a high-waisted or high-rise style for sleeping and long sitting, so the absorbent layer reaches where the flow pools.

Prevent it

Most leaks never happen if you:

• Match the pair to your real flow, not the label word.
• Get the hip size right for each brand, and size up when between.
• Change before the pair is saturated on heavy days.
• Never use fabric softener, and strip wash if absorbency drops.
• Wear a high rise for overnight and long sitting.