Health guidance that follows the evidence
Clear answers about vaccines, infectious disease, and preventive care — drawn from randomized trials, large cohort studies, and systematic reviews. Every claim on this site is traceable to a source you can check yourself.
Vaccines & Immunization
The full childhood and adult schedules, what each vaccine prevents, the actual side-effect rates, and the evidence on the questions people ask most.
Read the schedules →Disease Reference
Measles, influenza, COVID-19, RSV, pertussis, and more — how they spread, who is at risk, what the complication rates really are, and when to seek care.
Look up a disease →Prevention & Screening
Which screening tests are worth doing and at what age, plus what the evidence actually supports on diet, exercise, sleep, alcohol, and tobacco.
See what to do and when →Evidence & Sources
How to read a study, why study design determines how much a result is worth, and the standing sources this site draws on.
Learn to check claims →What "following the evidence" means here
Health guidance is only as good as the reasoning behind it. These are the rules this site holds itself to — and they're the same rules you can use to judge any health claim, including the ones here.
Weight of evidence, not single studies
One study is a data point, not a conclusion. Recommendations follow when multiple well-designed studies — ideally randomized trials and large cohorts across different populations — converge on the same answer.
Absolute numbers, not just relative ones
"Doubles your risk" means little without knowing the starting risk. A jump from 1 in a million to 2 in a million is a doubling and is also almost nothing. Numbers here are given in absolute terms wherever possible.
Benefits and harms side by side
Nothing in medicine is free of downside. Real side effects are listed with their real rates, next to the benefit, so the comparison is yours to make rather than ours to assert.
Uncertainty stated plainly
Where the evidence is strong we say so. Where it's thin, contested, or still emerging, we say that too, instead of rounding it up to certainty in either direction.
Correction over consistency
Guidance changes when the evidence changes — that's the process working, not failing. Screening ages, dosing intervals, and risk estimates have all shifted in response to new data, and they will again.
No political frame
Pathogens don't have politics. Nothing here is written to support or oppose any party, official, or policy position. The question is always the same: what do the data show?
If you only read one thing
The interventions below account for an outsized share of preventable illness and early death. They are boring, extremely well supported, and widely under-used.
| Action | Why it matters | Evidence |
|---|---|---|
| Don't smoke or vape nicotine | Smoking remains the single largest preventable cause of death in the U.S. Quitting at any age adds years; quitting before 40 avoids nearly all of the excess mortality risk. | Very strong |
| Stay up to date on vaccines | Routine childhood immunization is one of the most cost-effective interventions in medicine. Adult flu, COVID-19, shingles, RSV, and pneumococcal vaccines prevent a large share of hospitalizations in older adults. | Very strong |
| Treat blood pressure | Hypertension is common, silent, and the leading modifiable risk factor for stroke. Treatment reduces stroke and heart-attack risk substantially, with inexpensive generic drugs. | Very strong |
| Do the recommended cancer screening | Colorectal, cervical, breast, and lung cancer screening each reduce deaths from those cancers in the populations where they're recommended. | Strong |
| Move regularly | 150 minutes a week of moderate activity lowers all-cause mortality meaningfully. The largest gains come from moving from nothing to something, not from doing a lot more. | Strong |
| Sleep 7–9 hours | Chronic short sleep is linked to cardiovascular disease, metabolic dysfunction, impaired immune response, and accident risk. | Moderate |
| Drink less alcohol, or none | Alcohol is a group 1 carcinogen. Risk for several cancers rises from low levels of intake; the once-claimed cardiac benefit of moderate drinking has largely failed to survive better study designs. | Moderate to strong |
This site is not a substitute for your clinician
General guidance describes what is right for most people most of the time. Your medical history, medications, pregnancy status, and immune status can all change what applies to you. Use this as preparation for a conversation with a clinician, not as a replacement for one.
If you are having a medical emergency, call your local emergency number (911 in the U.S.) now.
How this site handles change
Medical guidance has a shelf life. Every page carries a "last reviewed" date, and specific figures are attributed so you can check whether something newer exists. Where a recommendation has recently shifted — screening ages, vaccine intervals, dosing — the page says what changed and why, rather than quietly presenting the new number as if it were always the old one.
If you find something here that conflicts with current guidance from a major professional body, trust the professional body and treat this page as out of date.
Last reviewed: August 2026. This site summarizes evidence and recommendations from the professional bodies listed on the Evidence & Sources page. It is an educational resource and does not provide individual medical advice.