Allergies and Intelligence: Are Smart People More Allergic?
Allergies and intelligence are only weakly linked: top-2% scorers in UK Biobank had a few more allergies (31.5% vs 28.5%), and the link reverses in families.
Dr. Russell T. WarneChief Scientist
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People with very high intelligence do report slightly more allergies, but the link is small: in a UK Biobank study of about 250,000 adults, 31.5% of people in the top 2% for general intelligence reported an allergy, compared with 28.5% of everyone else. When researchers compare brothers within the same family, the best-studied allergic condition (eczema) goes with lower test scores, which points to family background as the main source of the raw association.
This article covers where the "smart people have more allergies" idea came from, what large population studies find, how allergy symptoms and drowsy medicines affect test performance, and why the confounds matter more than the correlation.
Where the "hyper brain, hyper body" idea came from
The idea has two sources: a 1980s study of extremely precocious students and a 2018 survey of Mensa members.
In 1986, Camilla Benbow reported that among students in the top 1 in 10,000 for mathematical or verbal reasoning, asthma and other allergies turned up at high frequencies, along with left-handedness and nearsightedness. She suggested a shared prenatal influence (testosterone) on the brain and the immune system. That hypothesis was speculative, and the students were an extraordinarily select group.
The modern version is Karpinski and colleagues (2018), published in the journal Intelligence. They surveyed 3,715 members of American Mensa, a society whose members have scored at or above the 98th percentile on an approved test, and asked them to self-report diagnosed or suspected conditions, including environmental and food allergies, asthma and autoimmune disease. The authors compared these rates with national statistics, found much higher rates in the Mensa group, and proposed a "hyper brain, hyper body" model in which high intelligence comes with heightened nervous and immune reactivity.
The design has two serious problems. Everything was self-reported, including "suspected" conditions that no doctor had diagnosed. And the respondents were self-selected twice over: they had chosen to take a qualifying test and join the society, and then chose to answer a health survey. Williams and colleagues (2023) made exactly this point, noting that people who seek out IQ testing or join high-IQ societies may differ from other high scorers in ways that inflate links with health problems. Comparing such a sample with national averages, with no matched control group, cannot tell you whether high intelligence itself is the cause.
What large population studies show
Better evidence comes from population samples in which everyone took the same test and health information was collected the same way for everyone.
The UK Biobank comparison
Williams and colleagues (2023) compared 16,137 UK Biobank participants whose general intelligence was at least 2 standard deviations above the population mean (roughly IQ 130 and up) with 236,273 participants in the average range. The high group had slightly higher odds of any allergy (31.5% vs 28.5%; odds ratio 1.13), driven by eczema (4.1% vs 3.2%) and "other allergies" such as food allergies (3.1% vs 2.6%). They did not have more hay fever or asthma.
The same study found that the high-intelligence group had less anxiety and less post-traumatic stress disorder than the average group, the opposite of what the Mensa survey implied for mental health (see our article on IQ and anxiety). The two groups did not differ in insomnia. So the most defensible part of the "hyper body" claim is a small excess of eczema and food-type allergies.
Sibling comparisons in Swedish conscripts
Swedish military conscription data let researchers test whether the allergy link survives a fairer comparison. Smirnova and colleagues (2019) studied 234,715 men examined at ages 17 to 20 between 1969 and 1976. Men diagnosed with atopic dermatitis (eczema) scored slightly higher on the conscription cognitive test, by 0.15 points on a 1-to-9 scale whose standard deviation was 2.0. That is about 0.075 standard deviations, or a little over 1 IQ point. After adjusting for the family's socioeconomic position and household crowding, the gap shrank to 0.06 and was no longer statistically significant.
Smith and colleagues (2024) then took the decisive step, analyzing 2,021,369 Swedish men and comparing brothers within the same families. In the sibling comparison, eczema was associated with poorer cognitive function. A sibling design holds constant much of what brothers share, including parental income, education, neighborhood and part of their genes, so the reversal suggests the original positive association came from family background.
Other cohorts
Results elsewhere point the same way. In Danish national registers, men with hospital-diagnosed eczema scored 0.60 points lower on the conscription intelligence test (366,182 men, 4,539 with eczema), a small gap on any plausible scaling of that test. In the British ALSPAC birth cohort, which gave children Wechsler intelligence tests at several ages, Sockler and colleagues (2024) found no clinically meaningful association between eczema and IQ; the one notable result was a Performance IQ about 2 points lower at age 8 among children with active moderate-to-severe eczema.
Asthma shows a modest negative link. A meta-analysis of 2,017 people with asthma and 2,131 healthy controls found small-to-medium cognitive deficits, largest in severe asthma and in patients from low socioeconomic backgrounds (Irani et al., 2017).
Allergy symptoms, antihistamines and test scores
Whatever allergies say about long-run ability, symptoms on the day can lower a score.
• Hay fever and exams: Walker and colleagues (2007) followed 1,834 UK students aged 15 to 17 from winter mock exams to summer national exams. Between 38% and 43% reported hay fever symptoms on any one exam day. Students with symptoms during the exam period were more likely to drop a grade in mathematics, English or science (odds ratio 1.4), and those who had taken a sedating antihistamine had higher odds still (1.7).
• Learning while allergic: in a classroom-style experiment, Vuurman and colleagues (1993) found that children with seasonal allergic rhinitis who were given a placebo learned less than healthy children, those given the sedating antihistamine diphenhydramine learned less still, and those given a non-sedating antihistamine came closer to, but did not reach, the healthy group.
These are temporary effects on performance rather than on underlying ability, but they matter for anyone taking an IQ test during pollen season. A score obtained while congested, sleep-deprived or drowsy from medication may underestimate what the person can do. Questions about which allergy treatment suits a particular person, including around exams, belong with a doctor, allergist or pharmacist.
Why the raw correlation misleads
Several things push allergies and test scores together without any biological "hyper brain" link.
• Family background: in the Swedish data, men with eczema more often came from families of office workers and less crowded homes, and adjusting for this removed the cognitive advantage. A British cohort of 5,834 adults also found that higher childhood cognitive ability predicted reporting eczema at age 50 (Cheng et al., 2017).
• Diagnosis and awareness: Williams and colleagues suggest that more intelligent people may be more aware of symptoms, have better access to health care, or live in more urban areas, where allergies are more common. Any of these would raise diagnosis rates without raising true prevalence.
• Self-selected samples: high-IQ societies, gifted programs and online surveys collect people who chose to be tested and chose to respond, which is why the Mensa estimates were so much larger than the UK Biobank ones.
For a wider look at the claim that very bright people are more sensitive or intense, see our article on high giftedness and personality.
Frequently asked questions
Are people with allergies smarter?
Not in any meaningful sense. People in the top 2% for intelligence report slightly more eczema and food-type allergies, but within families eczema goes with lower test scores, and the raw difference appears to reflect family background.
Did a study prove that high IQ causes allergies?
No. The 2018 Mensa survey that popularized the idea relied on self-reported diagnoses from a self-selected group and compared them with national averages, so it cannot show cause and effect.
Can hay fever lower your IQ score?
It can lower your score on the day. Hay fever symptoms and sedating antihistamines have both been linked to worse exam performance and slower learning, which is different from lowering underlying ability.
Is asthma linked to lower intelligence?
Slightly, on average. A meta-analysis found small-to-medium deficits on cognitive tests, mostly in severe asthma and in people from disadvantaged backgrounds.
Should I avoid taking an IQ test during allergy season?
If symptoms or drowsy medication are affecting you, testing on a better day will give a more accurate result. A doctor or pharmacist can advise on treatment.
The takeaway
The link between allergies and intelligence is real but small, and it is not what the "hyper brain, hyper body" headline suggests. Large population studies find only a few percentage points more eczema and food-type allergies among very high scorers, and the eczema link reverses when brothers are compared within families. The clearest practical effect runs the other way: active allergy symptoms and sedating medication can drag down performance on the day of a test. If you want a measurement taken on a good day, you can take the RIOT IQ test.
References
1. Benbow, C. P. (1986). Physiological correlates of extreme intellectual precocity. Neuropsychologia, 24(5), 719-725. [doi.org/10.1016/0028-3932(86)90011-4](. doi.org
2. Karpinski, R. I., Kinase Kolb, A. M., Tetreault, N. A., & Borowski, T. B. (2018). High intelligence: A risk factor for psychological and physiological overexcitabilities. Intelligence, 66, 8-23. [doi.org/10.1016/j.intell.2017.09.001](. doi.org
3. Williams, C. M., Peyre, H., Labouret, G., Fassaya, J., Guzmán García, A., Gauvrit, N., & Ramus, F. (2023). High intelligence is not associated with a greater propensity for mental health disorders. European Psychiatry, 66(1), e3. [doi.org/10.1192/j.eurpsy.2022.2343](. doi.org
4. Smirnova, J., von Kobyletzki, L. B., Lindberg, M., Svensson, Å., Langan, S. M., & Montgomery, S. (2019). Atopic dermatitis, educational attainment and psychological functioning: A national cohort study. British Journal of Dermatology, 180(3), 559-564. [doi.org/10.1111/bjd.17330](. doi.org
5. Smith, K. A., Hiyoshi, A., Vingeliene, S., von Kobyletzki, L., & Montgomery, S. (2024). Atopic dermatitis and cognitive function: A sibling comparison study among males in Sweden. British Journal of Dermatology, 190(4), 592-593. [doi.org/10.1093/bjd/ljae004](. doi.org
6. Vittrup, I., Andersen, Y. M. F., Skov, L., Wu, J. J., Agner, T., Thomsen, S. F., Egeberg, A., & Thyssen, J. P. (2023). The association between atopic dermatitis, cognitive function and school performance in children and young adults. British Journal of Dermatology, 188(3), 341-349. [doi.org/10.1093/bjd/ljac058](. doi.org
7. Sockler, P. G., Hooper, S. R., Abuabara, K., Ma, E. Z., Radtke, S., Bao, A., Kim, E., Musci, R. J., Kartawira, K., & Wan, J. (2024). Atopic dermatitis, cognitive function and psychiatric comorbidities across early childhood and adolescence in a population-based UK birth cohort. British Journal of Dermatology, 190(4), 501-509. [doi.org/10.1093/bjd/ljad486](. doi.org
8. Irani, F., Barbone, J. M., Beausoleil, J., & Gerald, L. (2017). Is asthma associated with cognitive impairments? A meta-analytic review. Journal of Clinical and Experimental Neuropsychology, 39(10), 965-978. [doi.org/10.1080/13803395.2017.1288802](. doi.org
9. Walker, S., Khan-Wasti, S., Fletcher, M., Cullinan, P., Harris, J., & Sheikh, A. (2007). Seasonal allergic rhinitis is associated with a detrimental effect on examination performance in United Kingdom teenagers: Case-control study. Journal of Allergy and Clinical Immunology, 120(2), 381-387. [doi.org/10.1016/j.jaci.2007.03.034](. doi.org
10. Vuurman, E. F., van Veggel, L. M., Uiterwijk, M. M., Leutner, D., & O'Hanlon, J. F. (1993). Seasonal allergic rhinitis and antihistamine effects on children's learning. Annals of Allergy, 71(2), 121-126. [pubmed.ncbi.nlm.nih.gov/8346863](. pubmed.ncbi.nlm.nih.gov
11. Cheng, H., Treglown, L., Montgomery, S., Kornilaki, E. N., Tsivrikos, D., & Furnham, A. (2017). The associations between personality traits, education, occupation and the occurrence of eczema in adulthood. Journal of Health Psychology, 22(7), 916-924. [doi.org/10.1177/1359105315618457](. doi.org
Hero image: Poaceae. - Phleum pratense, by Hectonichus, CC BY-SA 4.0. Via Wikimedia Commons.
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