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Medical sources

Every health claim on this site is checked against published research before it goes live. We open the paper itself and read what it says, rather than repeating someone else's summary of it.

52
sources
30
peer-reviewed studies
5
systematic reviews and meta-analyses
2002–2026
years of research

Those reviews are substantial: one pooled 43 studies covering 3,319 people, and another covered 29 randomised trials. The rest includes 3 clinical practice guidelines and patient guidance from the NHS, the American Academy of Pediatrics and the Cleveland Clinic.

For every claim you can also see what its source does not prove. That is the part most health sites leave out. 42 of our 50 claims carry a stated limit, six rest on evidence we describe as limited, and one is marked contested because good studies genuinely disagree. We would rather be useful to you than sound certain.

How we check

We open the original source and read what it says. A search snippet tells you where to look, never what is true: it routinely attributes findings to the wrong paper and drops the authors’ own caveats. When we cannot open a source, we cut the claim. We never publish a medication dose: guideline doses are adult doses, and an adult decides the medicine and the amount.

Verified
We opened the primary source and confirmed the claim appears in it, in this form.
Evidence is mixed
Good sources genuinely disagree. We say so rather than picking the more convenient one.
Limited evidence
A real source, but the researchers themselves flag small samples or low quality. We write "may", never "studies show".
How the body works
A standard, uncontroversial mechanism. We state it plainly and attach no study to it, because inventing a citation would be worse than having none.
No longer used
We published this and it was wrong. It is kept here so that we do not reintroduce it.

When to tell an adult

Heavy bleeding: signs to tell an adult about

Verified

Changing a pad or tampon every 1 to 2 hours, periods lasting more than 7 days, clots larger than about 2.5 cm, bleeding through to clothes or bedding, avoiding daily activities because of periods, and often feeling tired or short of breath.

What this does not support

Very heavy bleeding from the first period onwards can be the first sign of an inherited bleeding disorder, so it is worth raising even when everything else seems normal. The NHS page compares clot size to a 10p coin, which means nothing outside the UK, so we publish the measurement instead.

Checked 2026-08-28

Toxic shock syndrome: signs to act on

Verified

A high temperature or feeling hot, cold or shivery; muscle aches; a raised, sandpaper-like rash; flu-like symptoms. It can happen with a tampon or with a menstrual cup. Take the product out, say you were using one, and get urgent help.

What this does not support

Rare, but a reader will not recognise it unprompted, which is why we carry the signs in full rather than in summary. Pads and period underwear carry no toxic shock risk.

Checked 2026-08-28

Low mood: signs to tell an adult about

Verified

The NHS lists persistent sadness or low mood, irritability, loss of interest in things previously enjoyed, constant tiredness, sleeping too little or too much, appetite and weight changes, withdrawing from other people, feelings of guilt or worthlessness, emotional numbness, and thoughts about suicide or self-harm among the signs of depression in children and young people. It says to book a GP appointment if you think a child is depressed.

What this does not support

The NHS page gives the signs but no duration, so the two-week threshold comes from its general low-mood guidance rather than this page. Two house rules sit on top of this claim and are editorial choices rather than findings, recorded here so nobody later "corrects" them: we do not name suicide or self-harm in reader-facing copy, and we publish no country-specific helpline. Note that the evidence runs the other way on the first one. Dazzi 2014 reviewed 13 studies across adults and adolescents and none found a statistically significant increase in suicidal ideation from being asked about it; Gould 2005 found high school students asked about suicidality were less distressed than controls. What the WHO guidance actually warns about is describing a death or a method, which we never do. So the softer wording is a brand decision that keeps the route intact, not a safety improvement.

Checked 2026-08-28

Monthly tummy pain with no period yet

Limited evidence

An imperforate hymen, seen in about 1 in 2,000 females, typically shows up between ages 13 and 15 as cyclical abdominal pain with no period, in a girl whose other signs of puberty are well developed. Diagnosed late, it can lead to infection, kidney problems and endometriosis.

What this does not support

The source is a single case report with a literature summary, so it shows the presentation exists rather than how often monthly pain without a period has this cause. It is rare, and the point is the route to an adult, not alarm.

Checked 2026-10-06

Period pain

How common period pain is in adolescents

Verified

Reported between 16% and 93% depending on the population studied and how the question was asked, with severe pain in 2% to 29%.

What this does not support

The range is very wide because the studies are not measuring quite the same thing. Only the severe-pain figure supports saying that most girls do not have severe pain.

Checked 2026-08-12

Period pain in the general clinical picture

Verified

Dysmenorrhea occurs in 50% to 90% of adolescent girls and women of reproductive age.

What this does not support

A broad clinical-review figure, not a pooled estimate. It sits alongside the wider 16% to 93% range from De Sanctis, and neither of them is "the" number.

Checked 2026-08-28

When period pain usually starts

Verified

Primary dysmenorrhea begins an average of six to 12 months after the first period, matching the start of ovulatory cycles, and tends to recur with every cycle.

What this does not support

The same paper lists pain that arrives much later, or pelvic pain that keeps getting worse, along with abnormal bleeding or unusual discharge, as features of secondary dysmenorrhea. That is a different thing and it needs a doctor.

Checked 2026-08-28

Missing school because of period pain

Verified

One third to one half of those with period pain miss school or work at least once per cycle. Between 5% and 14% miss more often than that.

What this does not support

The figure is per cycle, not per month, and it describes girls who already have period pain rather than all girls.

Checked 2026-08-12

When pain relief works best

Verified

Most effective when started one to two days before bleeding begins and continued through the first two to three days, which tracks the peak in prostaglandins.

What this does not support

This is a timing principle only. We never publish doses: the amounts in clinical guidelines are adult amounts, and an adult decides both the medicine and the amount for a reader of a given age and weight.

Checked 2026-08-12

Why cramps happen at all

How the body works

The uterus is a muscle. Prostaglandins drive the contractions that shed the lining, and stronger contractions briefly reduce blood flow to the muscle, which produces pain. They also amplify pain signalling generally.

Checked 2026-08-12

What is normal in the first years

What a normal adolescent cycle looks like

Verified

Cycle length is roughly 20 to 45 days, averaging 32.2 days in the first two years after the first period. Most adolescents bleed for 3 to 7 days, and longer than 7 days is uncommon and merits evaluation. The 95th percentile for cycle length is 90 days even in that first year, so 90 days is the point at which absent periods are investigated.

What this does not support

ACOG puts the first-year range at 21 to 45 days. The one-day difference does not matter clinically, but it is a reason to write "roughly" rather than implying a hard boundary.

Checked 2026-08-28

Why the first cycles are so irregular

Verified

There is general consensus that in the first one to two years after the first period, the majority of cycles are anovulatory, meaning no egg is released.

What this does not support

The review says the path to ovulatory cycles remains undefined, that estimates span a broad range because methods and populations differ, and that girls move back and forth rather than progressing smoothly. That is why we publish the direction and not a percentage.

Checked 2026-08-28

The second reason to get cycles checked

Verified

Evaluation is suggested when the gap between periods persistently runs longer than 45 days, or when periods are absent for 3 months or more. Cycles typically do not exceed 45 days even in the first year after the first period.

What this does not support

Both triggers matter, not only the 90-day one. Someone whose cycles keep running 55 or 60 days meets a guideline trigger that the 90-day figure on its own would tell her to ignore.

Checked 2026-08-28

Whether pain relief stops working over time

Limited evidence

We found no source that tests or rules out a loss of effect from taking pain relief for a few days each month. The main dysmenorrhea review covers how well it works and when to take it, but says nothing about tolerance across cycles.

What this does not support

Absence of evidence is not evidence of absence. We can say there is no good evidence that it stops working. We cannot say that it definitely does not.

Checked 2026-08-28

When uneven early cycles need a check

Verified

Cycles vary from one to the next in adolescence. Hillard advises evaluation for cycles that are consistently outside the range of 20 to 45 days, and recommends that adolescents chart their bleeding from their first period.

What this does not support

The trigger is a consistent pattern, not one short or long cycle in an uneven run, and the paper does not treat change between cycles on its own as a reason for evaluation. It sits alongside the 45-day and 3-month triggers.

Checked 2026-10-23

Period products

What the menstrual cup evidence covers

Verified

43 studies with 3,319 participants. Cups hold 10 to 38 mL and are emptied every 4 to 12 hours depending on flow and cup type. Four studies (293 people) compared cups directly with usual products: leakage was similar in three and significantly less with cups in one. Three studies (370 women) that included a vaginal or cervical examination found no mechanical harm. Five cases of toxic shock syndrome were identified across the literature and the FDA database.

What this does not support

The review states that the quality of the quantitative studies was low, with only two of moderate-to-high quality. Quantitative and qualitative studies were graded on different scales, so no single quality figure covers all 43.

Checked 2026-08-28

How hard cups are to get used to

Verified

Pooled across all participants: about 3% could not insert the cup (1,251 people, 11 studies); 20.3% reported discomfort on insertion at first (1,061 people, 17 studies), which was 35.3% in the first cycle and 13.0% in later cycles; 12.6% found it uncomfortable to wear (32.9% first cycle, 7.9% later); and about 11% stopped using it (1,190 people, 10 studies).

What this does not support

These are pooled estimates across all ages, not an adolescent subgroup. Discomfort on insertion and discomfort in wear are two different outcomes. The 2-to-5-month learning curve reported alongside them comes from studies in low- and middle-income countries. Differences between the studies were very large.

Checked 2026-08-28

Nothing can get lost inside you

How the body works

The vagina ends at the cervix, and the opening in the cervix is far too small for a tampon or a cup to pass through, so an internal product cannot travel further into the body. The NHS puts it plainly: a tampon stays in the vagina.

What this does not support

Reassurance on its own is not enough. If it cannot be taken out, the next step is telling an adult, because a doctor or a clinic can remove it.

Checked 2026-08-28

How long an internal product can stay in

Verified

Change a tampon every 4 to 6 hours, and the AAP says every 4 to 8. Never leave one in for more than 8 hours. Empty a menstrual cup at least every 12 hours. Wash hands, and the cup, before use.

What this does not support

This has to travel with the toxic shock signs, not on its own. A post that teaches internal products and gives only wear times has told a reader to watch a clock without saying what she is watching for.

Checked 2026-08-28

How often to change a pad

Verified

NHS Wirral says disposable and reusable pads should be changed every 4 to 6 hours, depending on flow. Cleveland Clinic says to change pads or panty liners at least every 4 to 8 hours. On heavy days a pad needs changing sooner.

What this does not support

This is hygiene and comfort guidance, not a safety limit: the sources range from 3 to 8 hours and none gives evidence for one number. Pads carry no toxic shock risk. KidsHealth suggests every 3 or 4 hours as good hygiene, and changing sooner is never wrong. The only pad number that is a warning sign is needing a new one every 1 to 2 hours, which belongs to heavy bleeding.

Checked 2026-10-20

Swimming without an internal product

Verified

Swimming on a period is possible with a tampon, a menstrual cup, or reusable period swimwear. Period swimwear means not having to insert anything. Pads do not work in water.

What this does not support

Many readers are 9 to 12 and not ready for an internal product. Telling them they need one reads as "no swimming for you".

Checked 2026-08-28

When putting a tampon in hurts

Limited evidence

A microperforate or septate hymen, a transverse vaginal septum, and vaginismus can each show up as pain on inserting a tampon, or as not being able to insert one at all.

What this does not support

The source is a single case report, and one whose main subject is an ovarian tumour found by chance. It shows that a hymen variation can present this way. It is not a study of how often any of these conditions explain painful insertion.

Checked 2026-08-28

Symptoms across the cycle

Why bloating turns into loose stools

How the body works

Progesterone relaxes smooth muscle, including the gut, which slows things down in the second half of the cycle. Prostaglandins then speed things up around the period itself, which is why bloating often turns into looser stools on day one.

Checked 2026-08-12

Muscle soreness across the cycle

Evidence is mixed

A meta-analysis of 19 studies found that delayed onset muscle soreness and strength loss were greatest in the early follicular phase, meaning the days of bleeding, and lowest mid-luteal. Against that, a 2011 study found that interleukin-6 and delayed onset muscle soreness did not vary across the cycle at all.

What this does not support

The comparison that has actually been studied is early-follicular against mid-luteal. The few days just before bleeding, which is when girls most often report aching, are not well studied.

Checked 2026-08-12

Why period blood turns brown

How the body works

Iron in blood oxidises on contact with air, so blood that leaves the body slowly looks brown or rust coloured. Flow is slowest at the start and the end of a period, which is when brown is most often seen.

Checked 2026-08-12

Doing normal things on your period

Verified

Having a period does not by itself stop anyone doing normal things. NHS Wirral says that with a tampon, a menstrual cup or reusable period swimwear you can swim just like any other day, and suggests light movement such as stretching or walking for cramps.

What this does not support

Being stopped is a red flag, not a personal failing. NHS Wirral says to see a doctor if pain is severe or affecting daily life, and Cleveland Clinic lists severe cramping that keeps you from your usual activities as a reason to seek care.

Checked 2026-08-28

Vaginal discharge: what is normal and what to mention

Verified

The NHS describes normal discharge as clear or white, thick and sticky or slippery and wet, without a strong or unpleasant smell. It advises getting help for a change in colour, smell or texture, much more discharge than usual, itching or soreness, pain when peeing, or pelvic pain.

What this does not support

The page is written for adults and does not address girls before puberty or before a first period. Several of the causes it lists are sexually transmitted, which is why reader-facing copy gives the signs and the route to an adult rather than the causes.

Checked 2026-10-06

Migraine and headache

Sleep

Supplements

Dreams

What shapes the content of dreams

Verified

A semantic analysis of 1,687 dream reports and 1,679 waking reports from 207 Italian adults over 15 days, plus a separate dataset of 80 people during the 2020 lockdown. Stable traits, meaning attitude toward dreaming, tendency to mind-wander and perceived sleep quality, selectively influenced dream content. Lockdown dreams contained more references to limitation and higher emotional intensity, easing in later years.

What this does not support

Italian adults with a mean age of 34.9, not adolescents. The "experiences" half of the conclusion rests on the separate 80-person lockdown sample, not the 207. The authors state the analyses cannot establish cause and effect, and the paper explicitly rejects the idea that dreams directly replay waking life.

Checked 2026-08-28

Dreams and the menstrual cycle

Limited evidence

A small literature links cycle phase to dream content and recall. A cross-sectional questionnaire study of 944 healthy women found pleasant dream content associated with the luteal phase, at p = 0.038. The authors make no predictive claim.

What this does not support

Cross-sectional, self-reported, a borderline p value, and confounders that were not measured. What is genuinely unsupported is any dream predicting when a period will arrive, and none of it can apply before the first period.

Checked 2026-08-28

Talking about periods, and stigma

Talking beforehand and feeling prepared

Verified

Of 405 Mexican girls aged 12 to 15, only 39% felt prepared for their first period. Those who had talked about the emotional side with their mothers beforehand were about 3.45 times more likely to report feeling prepared.

What this does not support

A single-country sample. "Girls who talked about it beforehand felt more prepared" is safe to say. A precise universal figure is not.

Checked 2026-08-12

How people react to a visible period cue

Verified

When a woman dropped a tampon rather than a hair clip from her bag, observers rated her as less competent, liked her less, and tended to sit further away.

What this does not support

Useful for showing a reader that the discomfort is cultural rather than something about her.

Checked 2026-08-12

Rules that appear at home after a first period

Verified

Girls described being taught new codes of conduct after their first period: how to sit and behave, not playing with or talking to boys, not entering the puja room, not cooking for others, covering up more, and not going out unaccompanied. The authors report that the relationships most affected were those with the men in the girls' lives, including fathers, cousins and neighbours.

What this does not support

10 girls averaging 14 years old, in one rural community. It documents that this experience exists and has been recorded. It is not a description of any culture, family or reader.

Checked 2026-08-28

Menarche and pubertal timing

The age a first period arrives

Verified

There is no single age. StatPearls gives a typical range of 10 to 16 with an average of 12.4 years. Cleveland Clinic says most get their first period between 11 and 14, but that it can be anywhere from 9 to 15 or later. The NHS puts the average at about 12 and says it can start as early as 8.

What this does not support

This describes a population and is never a prediction for one reader. The boundaries are what matter: Cleveland Clinic says to contact a provider for a period before age 9 or no period by 15, and the NHS says see a GP if periods have not started by 15, or by 13 with no other signs of puberty.

Checked 2026-08-28

When puberty signs count as early

Verified

The NHS says that if signs of puberty start before the age of 8, this could be early puberty, that it is usually nothing to worry about, and that tests can find out if a condition is causing it. The Merck Manual gives the traditional definition as sexual maturation beginning before age 8 in girls.

What this does not support

The 8 line is for the first signs, such as breasts or pubic and underarm hair, not for a first period, which has its own line: Cleveland Clinic says to see a provider for a period before age 9. Merck notes these traditional standards are being reevaluated because puberty is starting earlier, especially in girls in the United States.

Checked 2026-10-20

How many girls have started by each age

Verified

In a US national survey of women aged 15 to 44 (2013 to 2017), the median age at first period was 11.9. 10% had their first period by age 10, 53% by age 12 and 90% by age 14.

What this does not support

One country, and based on adult women remembering how old they were, so the ages are approximate. It describes a population and is never a prediction for one reader, and the limits in "The age a first period arrives" still apply.

Checked 2026-10-08

What a first period usually looks like

Verified

A first period is often light. The NHS says it is not a sudden gush and that you will just see a reddish-brown stain, that it might not last very long, and puts a whole period at about 20 to 90 mL, roughly 1 to 5 tablespoons. Cleveland Clinic describes red or brown blood that is light at first, gets heavier, then becomes light again.

What this does not support

One common presentation, not the rule. A first period that is red and heavier is not automatically abnormal, and this must never be written so that a heavier first period sounds wrong. Heavy bleeding from the first period onwards still needs the heavy-bleeding signs.

Checked 2026-08-28

How long after breast growth a first period comes

Verified

The NHS and Cleveland Clinic both say a first period typically comes about 2 years after the breasts start growing. Cleveland Clinic lists cramping, bloating, tender breasts, acne, mood swings and tiredness as things that may be noticed in the days leading up to a first period.

What this does not support

An average, not a countdown. In a large British cohort the median ages imply a gap nearer 3.3 years, and age at first period ranged from 7.6 to 14.9. The symptoms listed are for the days just before, not months of practice cramps.

Checked 2026-10-06

The growth spurt and the first period

Verified

In 793 Swedish girls followed through puberty, the first period came on average about 1 year after peak height velocity, the point of fastest growth (1.05 years, SD 0.99), ranging from 2.81 years before to 5.04 years after. For 12% it came before the growth peak.

What this does not support

One Swedish cohort, and the growth peak is fitted from a growth model, so it can only be seen looking back. The authors say this may imply a looser relation between growth and the first period. The spread is far too wide to time a first period in months from height.

Checked 2026-10-23

Discharge before a first period

Limited evidence

Nemours KidsHealth says that about 6 months to 1 year before a first period, the body may start to make vaginal discharge, and that this is normal and due to changing hormone levels. It lists itching, a strong bad smell, or a colour change to brown, gray or green as signs to see a doctor.

What this does not support

A patient-education page that cites no study, so the timing is a rule of thumb rather than a measured interval. It does not say to tell a parent; our route is a trusted adult.

Checked 2026-10-23

Every source

Menarche and pubertal timing

Background reading behind our quizzes. It does not yet back a specific claim in the list above.

None of this replaces seeing a doctor. If something worries you, talk to an adult you trust and to a doctor.