Forget your star sign. Here’s a less common, better-documented question: what does the weather on the week you were born say about you?

In 2015, researchers at Columbia University pulled the medical records of 1.7 million patients born in New York between 1900 and 2000 and ran an algorithm hunting for diseases that correlated with birth month. 

They found 55 conditions dependent on birth month. The conclusions weren’t mystical, it’s that the season you’re born into can measurably shift your lifetime disease risk, because of what that season does to your body in its first few months of life. 

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What your first few months decide

An infant's immune system spends the first months of life learning what to treat as a threat. Whatever allergens happen to be floating around during that window — pollen, dust mites and mold — can shape that decision for years. 

The evidence goes back to 1983, when researchers found that babies born in seasons with heavier dust mite activity carried a 40% higher risk of developing dust-mite-related asthma. Later research confirmed the broader pattern: allergen sensitization during infancy raises lifetime allergy risk.

One study found babies born in fall face a 9.5% risk of food allergies, compared to 5% for babies born in June and July — and that babies born in November or December were three times more likely to develop eczema and wheezing. 

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A 2024 study of nearly 50,000 children's records in Moscow found allergic rhinitis was significantly more common in kids born October through April versus July.

It may be written in your genes

The effect goes deeper than symptoms, it may be written into gene expression itself. 

Researchers at the University of Southampton found epigenetic markers, chemical tags attached to DNA, linking birth season to allergy and eczema risk, tags that can influence how genes behave for years, and possibly even pass to the next generation. 

As lead author Gabrielle Lockett put it: it sounds like a horoscope by the seasons, except now there's real science for how that horoscope might actually work.

It affects more than allergies

The pattern shows up well beyond allergies, too. Moderate to severe nearsightedness peaks in babies born during summer months. 

Birth season has documented associations with ADHD and respiratory syncytial virus, and, in the most-replicated finding in the field, an elevated schizophrenia risk for people born December through March in the Northern Hemisphere. The proposed drivers are seasonal: vitamin D availability from sunlight, infectious exposure, maternal nutrition.

There are caveats, though

This is science, not fortune-telling, so it comes with real limits. First, these effects are small at the population level and several studies have found no clear association at all. 

Second, the pattern moves with the climate: the Columbia team found the asthma effect in New York sits two months off from the same effect in Denmark, tracking the two countries' different peak-sunshine seasons.

If the pattern shifts when the climate shifts, the cause isn't the calendar. It's the weather.

And that weather is on file

NOAA's National Centers for Environmental Information keeps historical temperature, precipitation, and snowfall records for individual stations going back decades, searchable through its Past Weather Tool. Enter a city, address, or zip code, pick a nearby station, and set a date.

So before you check your horoscope, try this instead: look up the weather on the actual day you were born. It won't tell you your future, but it's a recorded fact about the environment that helped shape your immune system before you could form a memory of it — which is a stranger and better story than anything in the stars.