Where it landed tells you what went wrong. That's most of the diagnosis, and once somebody pointed it out to me I stopped guessing at brands and started fixing the actual problem.
Where did it land?
Four locations, four causes, and they very rarely overlap.
- Up the back. She has been lying flat, and the liquid has pooled at the rear. Fasten the back waistband higher than the front, and size up if it's happening every night.
- Out of the legs. The leg cuffs are tucked in. Run a finger around each leg after fastening so the ruffle stands out. This is the most common leak of all and the easiest to fix.
- Out of the front. Almost always a boy, and almost always because the penis was pointing up. Point it down before fastening.
- At the waist, sides, or everywhere at once. The diaper is saturated, so this is a capacity problem, a longer interval than the size can handle, or a size too small.
| Wet patch | Usual cause | Fix |
|---|---|---|
| Around the thighs | Leg cuff tucked inward | Run a finger round each cuff to pull the frill out |
| Up the back | Back panel too low, or loose stool | Pull the back higher than the front before fastening |
| Up the front, boys | Penis pointing upward | Point it downward before fastening |
| Everywhere, saturated | Left on too long, or too small | Shorter interval, or size up |
| Sides, with gaps you can see | Too big | Size down; check the tabs meet symmetrically |
| Only overnight | Long stretch plus air-con | See the overnight guide: different problem |
How to check the fit properly
Thirty seconds, after every change for a week, and you'll find the problem. Two fingers should slide flat under the waistband. The leg ruffles should stand up and out, all the way round. The front panel should be smooth with no fold running through the core. The back should be higher than the front. And there should be no red marks anywhere when you take it off. Tighter is the instinct and it's the wrong move, because pulling the waistband tight flattens the leg cuffs against the skin, which is exactly what creates the channel the liquid escapes along.
Is it the size, and which way?
Up, nearly always. This is the one that catches people, because a leak feels like something is too loose.
Diaper sizes overlap by design, and the higher size holds more. If she's at the top of the weight range for her size, or the tabs are meeting close to the middle, or there are red marks in the morning, go up. Capacity is the reason.
Size down only when the diaper is visibly gaping at the legs, the tabs are overlapping past the panel, or she's well below the weight range. That's much rarer.
Weight ranges are a guide. Two babies at the same weight can be entirely different shapes, and a chubby-thighed baby in the correct weight range may still need the size up for the leg fit alone. Richard and Charles were never in the same size at the same age despite similar weights.
On sizing
When the fit is right and it still leaks
Then look at the interval, the position and the product, in that order.
Stretch first: eight hours in a diaper rated for a daytime change will leak whatever the fit. Position second: side-sleepers leak sideways, back-sleepers leak up the back. Then the product. Some diapers have more absorbent core than others at the same size, and overnight versions exist for a reason.
I'd also check the obvious things people are embarrassed to ask about. A diaper put on backward leaks immediately. Cream applied thickly can waterproof the inner surface so it repels instead of absorbing, which is a common cause. A diaper that's been in a hot bag all afternoon performs worse than one from the cupboard. I think the adhesive goes. I could be wrong about the mechanism.
Mentioned above
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Maison Q Blanket & Wash Cloth BundleS$99.00Shop nowWhen a leak is a health signal
Rarely, and these are the versions to act on.
- A sudden jump in volume alongside increased thirst, which wants a same-day check.
- Watery, very frequent stools, which no diaper is built to contain and which can dehydrate a baby quickly.
- Blood or mucus in the stool.
- Dark, strong-smelling urine, or noticeably fewer wet diapers, which is the opposite problem.
- A rash that appeared with the leaking and isn't settling, since urine against skin is doing the damage.
- A toddler previously dry at night who has started leaking again, particularly with any pain or fever.
If it is nights or stool
What other parents wanted to know
Why does my baby's diaper keep leaking?
Usually a leg cuff tucked inward, or a size that is too small or too big. Check the cuffs first. The elastic frill should sit outside against the skin, not folded in.
Does a leaking diaper mean the wrong size?
It can go either way. Too small leaks as a flood with red marks at the waist; too big leaks as a trickle through visible gaps while the diaper still feels light.
Why does the diaper leak up the back?
The back panel is sitting too low. Pull the rear waistband noticeably higher than the front before fastening. That's also the main fix for blowouts.
Why does my baby boy's diaper leak at the front?
The penis is pointing upward inside the diaper. Point it downward before fastening and front leaks usually stop entirely.
Should I change diaper brand if it keeps leaking?
Last, not first. Check leg cuffs, waistband height, tab symmetry and size before assuming the diaper is at fault. Cut varies more than quality between brands.
What I read for this
This guide is general information, written to help you understand a topic and ask better questions. It is not medical advice and does not replace your own doctor, midwife or paediatrician. Anything that worries you about your baby belongs with them.