You chose a period panty precisely so you wouldn't have to check your pants every hour... yet, a leak appears around the groin or on the side of the panty.
The situation is frustrating, but far from exceptional.
Contrary to what one might think, a side leak does not automatically mean that the period panty is of poor quality or that it does not absorb enough. Several very different phenomena can cause exactly the same result: a size that is slightly too big, a panty that is too tight, a particularly rapid flow, an absorbent zone that does not match your body shape, saturation, poor distribution of blood when you are sitting or lying down, or a progressive loss of absorbent performance related to care.
A period panty works thanks to several technical layers that, depending on the model, can wick moisture, hold the flow, and limit its passage onto clothing. The absorption levels also vary from one model to another.
But for this system to be effective, the blood must arrive on the absorbent zone and have time to penetrate it.
This is precisely where the key to side leaks lies.
So, why is your period panty leaking even though it seems far from being completely soaked? How can you distinguish between a poor fit and insufficient absorption capacity? And above all, how can you prevent it from happening again?
How does a period panty really work?
To understand a leak, you must first understand what you are asking a period panty to do.
A period panty externally resembles a classic undergarment, but its crotch generally includes several layers with complementary functions.
The first layer, located in contact with the skin, allows the liquid to quickly travel toward the absorbent layers while trying to maintain a relatively dry feel.
The intermediate part retains the menstrual flow.
Finally, a waterproof or fluid-resistant layer acts as a final barrier before the outer fabric and clothes. The exact composition and number of layers vary by manufacturer and model.
However, protection is not identical across the entire surface of the panty.
It is primarily the absorbent gusset, meaning the reinforced area located in the crotch that may extend forward or backward, that collects the flow.
If the blood reaches this area directly, it is gradually absorbed.
But if it flows to the side, if the panty gaps around the groin, or if a large amount of blood arrives suddenly faster than the fabric can absorb it, the liquid can reach the edge of the protective area and create a side leak.
This is why two people wearing exactly the same period panty with a seemingly comparable flow may have a very different experience.
Period panty leaking on the sides: the main causes
There are several possible causes. Before changing models or absorption levels, it is useful to observe when, where, and under what circumstances the leak occurs.
A leak that happens after eight hours of wear probably does not have the same origin as a leak appearing after thirty minutes.
Similarly, a leak that occurs only at night does not necessarily have the same cause as a leak during a day at the office or during exercise.
1. The period panty is too big
This is one of the first things to check.
A period panty must fit the body correctly, especially around the crotch and thighs.
If it is too big, a small gap may appear between the fabric and the skin around the groin. The blood can then naturally follow this path and reach the edge of the panty before it has even been absorbed.
You may therefore notice a side leak even though the center of the absorbent zone still seems relatively dry.
Certain signs may alert you:
the panty slips down slightly when you walk;
you have to reposition it regularly;
it forms wrinkles around the crotch;
the leg openings do not stay in good contact with the skin;
the gusset seems to move when you sit or stand up.
In this situation, increasing the absorption may not solve the problem.
It is better to check the size first.
The size indicated on your usual underwear is not always enough. A period panty has several technical layers and its elasticity may be different from that of classic underwear.
Take your measurements around the waist and especially the hips, then compare them to the size guide for the model in question.
2. But a panty that is too small can also cause leaks
Conversely, choosing a smaller size thinking that a very tight panty will prevent leaks is not a good strategy.
When the panty is too small, the gusset may be excessively tight. It then fits the body less naturally and may shift or crease.
The elastic can also compress the groin strongly and create a path toward which the liquid is directed.
A panty that is too small is generally recognizable by some simple signs:
it leaves strong marks on the skin;
the elastic cuts around the thighs;
the waistband compresses the stomach;
the crotch seems pulled forward or backward;
you feel discomfort when you sit;
the panty seems comfortable while standing but becomes too tight when you move.
The correct size is therefore the one that allows for a sufficiently close fit to keep the protection in place without excessive compression.
The garment must support the body, not restrict it.
To learn more, consult our guide How to choose the right size period panty?
3. The absorbent zone is not positioned where your flow is draining
We are not all the same, and menstrual flow does not distribute exactly the same way in every woman.
For some, the blood is mainly collected in the center of the crotch.
For others, it tends to move more toward the front.
For yet others, it drains more toward the back, especially when sitting or lying down.
The vulvar morphology, posture, movements, and pelvic position influence this distribution.
A panty can therefore have excellent absorption capacity while being less suitable for a person if its protective zone is too narrow or does not extend far enough in the direction of their flow.
This is particularly easy to identify when the leak always appears in the exact same spot.
If the center of your panty is not very wet, but you regularly observe a leak on the same edge, you should consider a problem with the positioning or width of the absorbent zone rather than a general lack of absorption.
4. Your period panty is saturated
Another very common scenario: the panty functions perfectly for several hours and then suddenly starts to leak.
In this case, it may have simply reached its maximum capacity.
A period panty cannot absorb an unlimited amount of liquid.
Different absorption levels exist precisely because the needs are different between a very light start of a period, a day of moderate flow, and the heaviest hours of the cycle.
When the absorbent part is saturated, the blood naturally seeks another direction.
It can then move laterally and reach the seams or the leg openings.
It is somewhat the same phenomenon as with a soaked sponge: when it reaches its maximum capacity, the excess liquid can no longer be retained properly.
One clue often helps identify this situation: the leak appears after several hours of wear and the absorbent zone is widely wet.
The solution is then to change the panty sooner or to choose a higher absorption level on the heaviest days.
It is not necessary to use the same model throughout the cycle.
A combination of panties for light flow, moderate flow and heavy flow allows you to adapt the protection to the different phases of menstruation.
Also, find our article dedicated to different menstrual flows and choosing the right absorption level.
5. Your flow is very rapid: the panty doesn't have time to absorb
Here is an important nuance.
Absorbent capacity and absorption speed are not exactly the same thing.
A panty may still have significant capacity but still leak if a large amount arrives suddenly in the same spot.
Some women experience this phenomenon after sitting or lying down for a long time. A small amount of blood may accumulate in the vagina and then be rapidly expelled when standing up.
This phenomenon explains that familiar feeling of a "wave" or a sudden discharge.
If the fabric receives a large amount of liquid in a few seconds, some may move on its surface before having time to penetrate the absorbent layers.
It may then reach the sides.
This type of leak is particularly common during hours when the flow is heaviest.
A more absorbent model, with a sufficiently wide protective zone, may be better suited for these days.
If you have to change protection very frequently, if your periods regularly stain your clothes or bedding, or if you have to combine multiple protections to manage your daily life, your flow may also be considered particularly heavy. The NHS recommends consulting a doctor when very heavy periods affect daily life; the need to change certain protections every one to two hours is one of the signs to consider.
Find our file on heavy periods: how to know if your flow is normal?
6. The leak mainly appears while sitting
You may sometimes wear your panty all morning without a problem and discover a leak after several hours at the office, in the car, or in class.
The sitting position slightly changes the shape of the pelvis and the way the gusset sits against the body.
The blood may also be directed more toward the back or to one side.
The phenomenon is even more pronounced when remaining still for a long time.
If leaks occur mostly when you are sitting, observe their location precisely.
A leak toward the back may indicate that the absorbent part would benefit from being positioned higher.
A repeated side leak may indicate that the gusset is not positioned well enough against your body shape when seated.
It may be interesting to test your panty at home by alternating walking, sitting, and lying down to determine when the leak occurs.
7. Why does my period panty leak at night?
Nighttime is a special case.
When you are standing, gravity naturally directs the flow downwards.
When you sleep on your back, stomach, or side, the blood may move differently.
On your back, it may drain more toward the back.
On your stomach, it may move toward the front.
On your side, it may accumulate preferentially on one of the edges of the absorbent zone.
This is why a panty perfectly suited for the day may sometimes show its limits overnight.
Wear time also plays a role: eight hours of sleep corresponds to a long period without changing protection.
Practical recommendations regarding period panties emphasize that wear time depends on the flow: a panty must be changed more frequently during the heaviest hours.
For the night, therefore, prioritize:
an absorption level that matches your nocturnal flow;
an absorbent zone long enough toward the back;
a shape that stays in place when you move;
and possibly a high-waisted or more enveloping model if you tend to change positions a lot.
If your period is particularly heavy, keep a clean panty nearby so you can change it if necessary.
8. Physical activity can slightly shift the panty
Walking, running, cycling, squatting, practicing yoga, or simply going up and down stairs places enormous strain on the fabric around the groin.
A properly fitted period panty should normally follow these movements without losing its positioning, but a poor fit or a cut that is not suited to your body shape can promote movement.
The panty may then:
rise;
rotate slightly;
form a wrinkle;
shift in the crotch area.
The blood then arrives partially outside the optimal absorption zone.
For sport, support is almost as important as absorption.
Perform some movements while trying it on: sit, squat, walk, and lift your legs.
The panty must stay in place.
9. The absorbent crotch may be too narrow for your body shape
The width of the crotch varies depending on the period panty models, just like classic underwear.
Yet a narrow zone can be perfectly suited to one person and insufficient for another.
If your flow regularly falls near the edge of the absorbent zone, a few millimeters can make a real difference.
You can check this after wearing your panty.
If the wettest area is systematically located near a seam or edge, your body shape or natural way of standing may require a slightly wider protection.
Users also regularly mention the width of the gusset when they experience side leaks, even with a panty that is not completely saturated.
This is not a problem with your body.
Not all classic panty cuts suit all body types; the same applies to menstrual protection.
10. Your period panty is no longer absorbing as well as before
A panty that worked perfectly for several months and suddenly starts leaking deserves further analysis.
The question to ask is:
what has changed?
If your flow and body shape are similar, check the care of your panty.
Some products can gradually alter the properties of the absorbent fibers.
Fabric softener is particularly discouraged for absorbent textiles. It deposits substances on the fibers intended to make them softer, but these substances can reduce their ability to quickly absorb liquid.
It is advisable to use a mild detergent and to air dry.
An excessive accumulation of detergent can also leave residues.
Therefore, always follow your manufacturer's washing instructions.
You can find all our advice in our guide How to wash a period panty without reducing its absorption?
11. Also pay attention to drying
Drying is a sometimes overlooked step.
Excessive heat can, depending on the model's composition, weaken certain elastic fibers or waterproof layers. This is why natural drying is generally preferred for this type of product.
A panty must also be perfectly dry before being worn or stored.
When several panties are used in rotation, it is therefore useful to have enough to allow each one to dry completely between uses.
12. What if the panty is actually defective?
This possibility should not be ruled out.
A leak that appears almost immediately through a seam when:
the panty is new;
the flow is light;
the size is suitable;
the absorbent zone is correctly positioned;
and the fabric is still almost dry,
may reveal a localized manufacturing or sealing problem.
Examine the starting point of the leak precisely.
If the liquid seems to pass systematically through the exact same seam while the rest of the absorbent zone remains dry, contact the seller to explain the problem.
Photos of the garment after washing and drying may help the customer service department understand the area in question.
How to know exactly why your period panty is leaking?
There is a very simple method: observe the time and place of the leak.
Leak almost immediately
If the leak appears quickly while the panty is not very wet, consider the following first:
the size;
the cut;
the gusset position;
its width;
or possibly a localized defect.
Leak after several hours
If the panty functioned for several hours before leaking, saturation is much more likely.
Try changing it one or two hours earlier during the next cycle.
If the leak disappears, you have probably found the cause.
Leak only on heavy flow days
Your absorption level may be insufficient for the heaviest days.
A period panty may work perfectly for the start and end of your period without being absorbent enough on the second day.
Simply adjust the protection level.
Leak only at night
Observe your sleeping position and the location of the stain.
If it is very far back or very far forward, opt for a model whose absorbent zone covers that area more.
Leak always on the same side
Examine the positioning of your panty.
Your pelvis, your posture, or your body shape may naturally direct more flow toward one side.
Also, check if the elastic on that leg is as snug as the other side.
Should I take a smaller size to prevent leaks?
Not necessarily.
This is probably one of the most common mistakes.
If the panty truly gaps around the thighs and moves when you walk, a smaller size may be appropriate.
But if it is already well-fitting, choosing smaller may instead cause compression and shift the gusset.
The rule is therefore to rely on measurements and the size guide, rather than the principle "tighter = more leak-proof."
A good period panty must stay in contact with the body without making you feel like you are wearing a shapewear item.
Should I choose a higher absorption?
Again, it depends on the cause.
If your panty leaks after several hours and seems widely soaked: probably yes.
If it leaks after twenty minutes while the absorbent zone is almost dry: probably no.
In the latter case, greater absorption will not necessarily change the trajectory of the blood.
You should check the size and the cut instead.
How long can you keep a period panty?
There is no universal duration that is valid for all women and all flows.
A panty can be worn longer on a light day than during the heaviest hours of the cycle.
Cleveland Clinic indicates that the duration depends on the flow and that a more frequent change may be necessary during the most important days; the same source advises against exceeding about twelve hours with the same panty.
NHS resources also mention a duration of about eight to twelve hours for period panties, to be adapted to the flow rate.
But the feeling remains a precious indicator.
If your panty becomes noticeably wet, heavy, or uncomfortable, do not wait for a leak: change it.
What to do when you have very heavy flow?
An occasional leak does not necessarily mean that your periods are abnormally heavy.
However, if you regularly soak through your protection despite an appropriate absorption level, the question should be asked.
Among the signs that may suggest very heavy periods are the need to change certain protections every one to two hours, frequent leaks on clothes or bedding, periods lasting more than seven days, or large clots. Significant fatigue or shortness of breath may also accompany excessive blood loss.
In this case, the goal should not just be to find an even more absorbent protection.
Talk to your doctor, midwife, or gynecologist to look for a possible cause.
Fibroids, adenomyosis, endometriosis, certain hormonal disorders, or certain life stages, particularly adolescence and perimenopause, can be associated with heavier periods.
Can I use a second protection with a period panty?
Yes, according to your needs.
Some people use the panty alone, while others prefer to use it as extra security with internal protection during particularly heavy flow days.
The period panty can therefore serve as:
primary protection;
emergency backup;
security for a long day;
or a complement to another method when it suits the person's preferences.
The essential thing is to find the solution that allows you to live through your period comfortably.
However, if you consistently need to combine multiple protections due to extremely heavy losses, talk to a healthcare professional.
Do teenagers have a higher risk of leaks?
First periods can make using a period panty a little more delicate, simply because the teenager does not yet know their flow.
They do not necessarily know which day will be the heaviest or how many hours their protection can last.
Furthermore, early cycles are often irregular.
A teenager may therefore think they have a light flow after a very discreet first day and be surprised by a much heavier day.
To start, it can be useful to test the panty at home or on a quiet day to learn how to recognize when it needs to be changed. Cleveland Clinic also advises testing a period panty in a reassuring environment and during a relatively light flow when discovering this type of protection.
To calmly prepare for first periods, find our article What to do if first periods arrive at school? as well as our selection of period panties for teenagers.
How to prevent period panty leaks: the right reflexes
A reliable period panty starts with a simple trio: correct size, proper absorption, proper care.
Before your next cycle, check your measurements and ensure the panty stays perfectly in place when you walk and sit.
Then, adapt the absorption level to the different days of your period rather than expecting the same performance from a light flow panty and a model designed for heavy days.
During the heaviest hours, change your panty before it is completely saturated.
For the night, observe in which direction your flow is moving and opt for a protection that is sufficiently long toward the front or back.
Finally, strictly adhere to the washing instructions: notably avoid fabric softener and washing or drying temperatures and methods not recommended by the manufacturer.
FAQ – Period panty leaking on the sides
Why is my period panty leaking even if it's not full?
When the absorbent zone is still relatively dry, a side leak may be due to a poor fit, gusset displacement, an absorbent zone that is too narrow for your body shape, or a very rapid influx of blood.
You must then observe the exact spot where the leak begins.
Can a too-big period panty leak?
Yes. If it does not fit the crotch and thighs well enough, blood may pass into the space between the body and the protection before being absorbed.
Can a too-small panty also leak?
Yes. An excessively tight underwear can stretch or move the gusset and alter the distribution of liquid. It must be fitted without compressing.
Why does my panty always leak on the same side?
The natural position of your flow, your body shape, or the way the panty sits on your pelvis may direct more blood toward that side.
Also, check that the leg opening remains properly fitted.
Why does my panty only leak at night?
The lying position changes the flow trajectory. Blood may move more toward the back, front, or side depending on your sleeping position.
A longer absorbent zone or higher absorption may then be necessary.
Why is my period panty leaking after several months of use?
If it worked before, check its care. Using fabric softener, certain detergent residues, or care that does not conform to recommendations can reduce the performance of absorbent textiles. Over time and washing, a panty also eventually wears out.
Should I wash a period panty before the first use?
Yes, when the manufacturer's instructions recommend it. An initial wash helps eliminate possible manufacturing residues and prepares the textile fibers for use.
Always consult the care label of your model.
What to do if my new panty leaks immediately through a seam?
If the size is suitable, the flow is light, and the panty remains almost dry, take a photo of the area in question and contact the seller. A localized manufacturing or sealing problem may be possible.
How many period panties should I prepare?
This depends on the period duration, the flow, the frequency with which you need to change, and the drying time between washes.
To exclusively use period panties, it is generally more comfortable to have several with different absorption levels rather than choosing a single model.
In conclusion, a side leak is often a precious clue
When a period panty leaks, the first reaction is often to think that it is not absorbing enough.
However, the location and time of the leak give much more information than the leak itself.
An immediate side leak while the panty is still dry points more toward a problem with the size, the cut, or the position of the absorbent zone.
A leak after several hours and a very wet protection suggests saturation.
A nocturnal leak may be related to body position.
A panty that worked perfectly before and is becoming less effective may invite you to review its care or consider gradual wear.
There is no single ideal period panty for all women, all days of the cycle, and all situations. The best protection is the one whose size, shape, and absorption level match your body and your flow.
Taking the time to observe your period over a few cycles usually helps quickly find the right combination.
And if your flow is so heavy that leaks are frequent despite using correctly chosen protections, do not consider it a fatality: talk to a healthcare professional.
At Adopte Ma Culotte, discover our period panties adapted to different flow levels to find the protection that matches your cycle, your body shape, and your daily life.