Published : 21 Sep 2026, 01:22 PM
Updated : 21 Sep 2026, 01:22 PM
Allergies are often associated with childhood, but they can emerge at almost any stage of life, sometimes after years without a reaction to a particular food or environmental trigger.
“Any person, at any point in their life, can develop a new allergy,” allergist Kelly Colas says.
Researchers are examining how infections, changes in the gut microbiome, hormonal shifts and even tick bites may contribute to new allergic reactions, the BBC reports.
When COVID-19 May Play a Role
Some people are genetically predisposed to allergies, but genetics alone does not explain why symptoms emerge.
“Often, something is turning it on,” says Ruchi Gupta, director of the Center for Food Allergy and Asthma Research at Northwestern University in Illinois.
COVID-19 may be one such factor.
A 2026 study found that people who had COVID-19 were at higher risk of later developing allergic rhinitis, commonly known as hay fever, and asthma.
“Infection increased the risk, and vaccination decreased the risk,” says study co-author Philip Curman, a dermatologist at Sweden’s Karolinska Institutet.
Curman says COVID-19 can strongly activate the immune system and increase inflammation associated with allergic disease.
Previous research has suggested that respiratory syncytial virus, or RSV, and rhinovirus may have similar effects, particularly in children.
Gupta says an immune system already occupied with fighting an infection may sometimes respond abnormally when it encounters food or environmental allergens.
When the Immune System Gets Confused
Some medicines may also be associated with later allergy risk.
Antibiotic use has been linked in some studies to a higher risk of allergies, possibly because the drugs can alter the gut microbiome — the community of microorganisms living in the digestive system.
The microbiome plays an important role in immune regulation. Disrupting its balance may contribute to what Gupta describes as “confusion in the immune system”, causing harmless substances to be treated as threats.
Hormonal changes can also affect allergy symptoms.
Pregnancy, for example, can significantly alter the immune system. Around a third of women with existing environmental allergies find their symptoms worsen during pregnancy, Colas says.
Some pregnant people with no previous allergies may also develop sneezing, congestion and a runny nose in a condition known as pregnancy rhinitis.
Pregnancy rhinitis is not generally considered a true allergy and usually disappears after delivery. Its exact cause is unclear, although hormonal changes are thought to play a role.
Research has also suggested that some women may develop new allergies around menopause, another period of major hormonal change.
The Tick Bite That Can Lead to a Meat Allergy
A bite from the Lone Star tick, found mainly in North America, can lead to an unusual form of food allergy.
The bite can sensitise the immune system to a sugar molecule known as alpha-gal, which is found in most mammals.
People with the resulting condition, known as alpha-gal syndrome, can develop allergic reactions after eating red meat or other mammalian products.
Symptoms can include hives, swelling and gastrointestinal problems and, in severe cases, more serious allergic reactions.
Thomas Platts-Mills, a professor of medicine and microbiology at the University of Virginia, helped establish the link between tick bites and alpha-gal syndrome.
He had been bitten by larval ticks after hiking and later developed hives after eating lamb. Blood tests subsequently showed high levels of allergy-related antibodies.
Cases of alpha-gal syndrome have become increasingly recognised in the US as Lone Star ticks have expanded beyond parts of their traditional range.
Can Sudden-Onset Allergies Be Reversed?
Some temporary allergy-like conditions, such as pregnancy rhinitis, disappear on their own.
But true allergies that emerge after illness, tick bites or other triggers may persist.
Allergies occur when the immune system mistakenly identifies a normally harmless substance as a threat and mounts a response against it.
Symptoms can range from a runny nose and itchy eyes to potentially life-threatening anaphylaxis.
There is currently no guaranteed way to reverse a newly developed allergy, Gupta says.
Researchers are nevertheless studying ways to prevent or reduce allergic reactions.
Scientists are examining whether changes to the gut microbiome could influence allergy risk, although more research is needed before measures such as probiotics or prebiotics can be considered proven preventive strategies.
They are also studying whether controlling excessive inflammation during viral infections could reduce the risk of later conditions such as asthma.
Immune-modulating drugs are another area of interest.
Omalizumab, sold under the brand name Xolair, has long been used to treat asthma and can also reduce the risk of allergic reactions after accidental exposure to certain foods.
Researchers are also exploring experimental approaches designed to retrain or moderate the immune response to allergens.
For now, sudden-onset allergies cannot always be prevented or reversed.
But researchers say a better understanding of how infections, hormones, gut bacteria and environmental exposures interact with the immune system could eventually lead to more effective prevention and treatment.
