Radiation

Cosmic radiation, explained: where it comes from, what the Sun does to it, and what you can do

July 26, 2026Updated October 20, 20268 min readFor pilots and passengers

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In this article

What it is
Why it can do harm
How much, compared with what
What sets the dose of a flight
Why a busy Sun means less radiation
Radiation from the Sun itself
What reduces it, and what doesn't
The rules

Every flight adds a small dose of cosmic radiation. For a passenger it is a footnote. For someone who flies for a living, it adds up to more radiation in a year than the average nuclear-industry or hospital worker receives on the job. Here is where that radiation comes from, why it changes from flight to flight and from year to year, and what you can and can't do about it.

What it is

Cosmic radiation is made of particles rather than light. Most of it starts as galactic cosmic rays, atomic nuclei moving at nearly the speed of light; close to nine in ten of them are protons, and most of the rest are helium. They come from outside the solar system, many of them accelerated by exploding stars, and they arrive from every direction, all the time.

These particles rarely reach us directly. When one hits the top of the atmosphere, it smashes into a nitrogen or oxygen nucleus and sets off a shower of secondary particles (neutrons, protons, electrons, muons and gamma rays) that collide with other nuclei in turn. The shower builds as it comes down, peaks well above airliner altitudes at roughly 50,000 to 65,000 feet, and then thins out as the air below absorbs it. The whole atmosphere weighs as much as a 10-meter layer of water, and by the time the shower reaches the ground most of it has been stopped.

Airliners cruise in the thick of it. On mid- and high-latitude routes at 35,000 to 40,000 feet, the dose rate is typically 2 to 5 microsieverts (µSv) an hour, roughly a hundred times what cosmic radiation delivers at sea level. Neutrons are the biggest contributor at those altitudes.

Why it can do harm

Cosmic radiation is ionizing. Each particle carries enough energy to knock electrons out of the atoms it passes, and inside a cell that can break DNA. The body repairs almost all of that damage. Once in a long while a repair goes wrong in a way that, years later, contributes to cancer.

Flight doses cause no symptoms, burns or sickness. The concern is a small rise in the lifetime chance of cancer, which radiation protection assumes grows in step with total dose, with no safe threshold. For protection purposes, the International Commission on Radiological Protection (ICRP) uses a nominal risk of about 5% per sievert (1,000 mSv), a figure that covers cancer and inherited effects together. By that yardstick, a 30-year long-haul career on polar routes at up to 6 mSv a year (the IAEA's upper figure for aircrew), or 180 mSv in all, adds about a 1 in 110 lifetime chance of dying of cancer, by ICRP's estimate. That is small but not zero, and it is why EU law manages aircrew exposure as occupational exposure.

An unborn child is more sensitive than an adult. ICRP's guidance is that once a pregnancy is declared, the dose to the embryo or fetus should stay below about 1 mSv for the rest of the pregnancy, the same figure as the yearly limit for the public.

How much, compared with what

Doses from flying and from medicine are both expressed as effective dose, in sieverts. Effective dose weights each type of radiation and each organ by how much harm it can do, which is what makes the numbers comparable.

Source	Dose
New York–London flight, July 2026 (LogAloft calculation)	about 0.03 mSv
Chest X-ray, two views (front and side)	0.1 mSv
Mammogram	about 0.4 mSv
CT scan of the abdomen	about 8 mSv
A year of flying as crew, worldwide average	about 2.7 mSv
A year in the nuclear industry, worldwide average	about 0.6 mSv
A year as a medical radiation worker, worldwide average	about 0.4 mSv

The bigger difference is how the dose arrives. An X-ray or CT scan is a single dose, given once for a medical reason. Cosmic radiation is a low dose rate that runs for as long as you are aloft and adds up over a career. Radio waves, cell phones, Wi-Fi and microwave ovens are another kind of radiation altogether. They are non-ionizing and lack the energy to break DNA.

What sets the dose of a flight

Altitude comes first. The higher you cruise, the less air sits above you, and the dose rate climbs quickly with every thousand feet.

Latitude matters nearly as much. Earth's magnetic field steers charged particles away from the equator and lets them in near the magnetic poles, and above about 55 degrees magnetic latitude it gives little protection. At the same altitude, the FAA puts the rate over the polar regions at about twice the rate over the geomagnetic equator.

Then there is time. Dose is rate multiplied by hours, so long flights at high latitudes add the most.

The fourth factor, the Sun, is the one that surprises people.

Why a busy Sun means less radiation

The Sun constantly blows out a solar wind, a thin stream of charged particles that carries its magnetic field out past the planets. That magnetized bubble shields the inner solar system, turning part of the galactic cosmic rays away before they reach Earth.

Solar activity rises and falls on a cycle of about 11 years. Near solar maximum the Sun has more sunspots, a stronger and more tangled magnetic field and a gustier solar wind, and the shield is at its strongest. Near solar minimum it relaxes and more cosmic rays get through. The effect is large. In LogAloft's calculations, the same New York–London flight gave about 41 µSv in October 2009, at the last solar minimum, and about 24 µSv in January 2026, a month of high activity near the current maximum.

By the sunspot record kept at the Royal Observatory of Belgium, the current cycle peaked in October 2024, and activity stayed high into 2026. As the Sun quiets toward the next minimum, likely around the end of the decade, the shield weakens and the dose on every route creeps up from year to year.

Radiation from the Sun itself

Very little of it reaches cruise altitude. The Sun's light, ultraviolet and X-rays are absorbed high in the atmosphere, and the particles of the ordinary solar wind are far too weak to get down to where airliners fly.

Solar storms are the exception, and they are more frequent around solar maximum. NOAA rates them on three scales, and each one touches aviation differently.

Solar radiation storms (S1 to S5) happen when a flare or a coronal mass ejection fires out high-energy protons. Most are too weak to change the dose at cruise. The rare, very energetic ones show up even in neutron monitors on the ground and are called ground level enhancements; 77 have been recorded since 1942. They can raise dose rates on polar routes for hours, and that is when airlines may send flights lower or away from the poles.

Geomagnetic storms (G1 to G5) come when a coronal mass ejection shakes Earth's magnetic field. The main aviation problems are HF radio and GPS, but the field's protection can also retreat a few degrees toward the equator for a while. The same event often lowers the galactic cosmic-ray count for a few days, because the passing cloud of solar material sweeps part of it aside.

Radio blackouts (R1 to R5) are caused by X-rays from flares. They disturb HF radio on the sunlit side of the Earth for minutes to hours and add no radiation at cruise.

Our article on solar storms and your flight covers the scales, the aviation advisories and the biggest events.

What reduces it, and what doesn't

There is no practical shielding inside an airplane. Stopping these particles takes meters of water or concrete. The fuselage and cabin make little difference, and no protective clothing helps. What you can do is know the dose and manage it.

Start with your own number. The dose depends on routes, altitudes and the Sun as well as on hours, so two crew members with similar logbooks can end the year far apart. LogAloft works out the dose of each flight and keeps a yearly and career total. On Pro, the dose comes from the track the aircraft actually flew; free accounts get that for flights between US airports, from the FAA's data, within the plan's limits. Otherwise the dose is an estimate along the route an airline would plan for that day's winds.

If you have some say over your schedule, mixing in lower-latitude flying keeps the yearly total down, since polar and long northern routes add the most. During a pregnancy, check what a schedule would add before you fly it. The FAA recommends keeping the dose to the unborn child to no more than 0.5 mSv in any month.

During the rare severe solar radiation storms, airlines may descend or reroute flights, guided by their own procedures and by the space weather advisories issued to aviation under ICAO rules.

The rules

In the European Union, where crew doses are liable to exceed 1 mSv a year, airlines must assess those doses, take them into account when building schedules so that highly exposed crew get less, tell crew members about the health risks and their individual doses, and apply the directive's pregnancy protections (Council Directive 2013/59/Euratom, Article 35). In the United States, FAA Advisory Circular 120-61B gives guidance for airline programs that inform crews about in-flight radiation, but no regulation requires an airline to measure or record a crew member's dose.

Sources

This is information, not medical advice. For questions about your own health or a pregnancy, talk to your doctor or aviation medical examiner.