Hangover or alcohol intolerance? How to tell the difference

Hangovers, aka the aftermath of drinking alcohol, have quite the shopping list of symptoms – headache, nausea, intense thirst, tiredness and brain fog.

But, some symptoms people assume are hangovers may actually be caused by alcohol intolerance or allergy.

While many of us enjoy an alcoholic drink, the bad news is alcohol's a toxic substance.

When we feel hungover, this is our body converting it into non-toxic substances. The length and severity of hangovers can vary, depending on the strength and amount of alcohol consumed, and the rate our body can process it.

Dehydration can also be responsible for our hangover symptoms, from headaches and fatigue to anxiety and sensitivity to light and sound, says Dr Timothy Watts, a consultant physician in adult allergy at The London Clinic.

People with alcohol intolerance often suffer from severe hangover-like symptoms due to a genetic metabolic disorder, external, which "causes the body to process or metabolise alcohol incorrectly," Watts says.

When we drink alcohol, an enzyme called aldehyde dehydrogenase (ALDH) helps us to recover and transform the toxins into acetic acid (aka vinegar!).

Older adults have less ALDH, which explains why hangovers can feel worse with age.

Those with a genetic intolerance have a mutated version of ALDH, which leads to more unpleasant symptoms, says Watts, such as "extensive skin flushing, nausea, vomiting, palpitations, headache and fatigue".

Some people are intolerant to the ingredients in alcohol, not the alcohol itself, such as histamine, external and salicylates, external (found in wine, beer, rum, and sherry).

Others, including up to 13% of asthmatics, external, are intolerant to preservatives in alcohol called sulphites.

Symptoms can include a stuffy or runny nose, headaches, hives, itchiness, wheezing and tummy upset, but reactions can be life-threatening, external.

Alcoholic drinks high in sulphites and/or histamine include wine, cider and beer. But, some varieties of gin and vodka, as well as natural wines are low in sulphites.

"A true allergy to alcohol is rare," says Doctor Fiona Sim, chief medical adviser for alcohol charity Drinkaware, external. "A person is much more likely to be allergic to one of the ingredients in their alcoholic drink, such as wheat, barley or another grain."

It's very difficult for consumers to know whether an alcoholic drink contains allergens or ingredients they're intolerant to.

In the UK alcoholic drinks manufacturers don't have to label ingredients or nutritional information, external.

Sim urges anyone who knows they're allergic to certain foods, particularly grains, to be aware they could be in drinks, too and to check before trying them.

This is particularly important if you drink cocktails or mixed drinks, which could have a long list of ingredients.

Alcoholic drinks can also trigger an allergic reaction to food if you consume the two together, as alcohol can interfere with the gut lining.

For example, someone with a wheat allergy may only react after eating wheat followed by drinking alcohol or exercising.

"Alcohol and sulphites tend to evaporate away during cooking, so the potential for intolerances is certainly reduced," Watts says.

But, if you're allergic to an ingredient found in certain alcoholic drinks, dishes which contain that drink are not safe to eat.

It's pretty simple to recognise the difference between a hangover and an alcohol intolerance, Watts says.

"Hangovers are usually in full effect the morning after a night of heavy drinking. Metabolic genetic intolerances happen more quickly, generally within an hour of drinking."

It's harder to identify the difference between alcoholic intolerance and allergy, because the symptoms can overlap. Some allergic reactions are almost instant but not all.

"If in any doubt, always consult a healthcare professional," Watts says.

"Investigations for alcohol reactions normally consist of specialised allergy blood tests, skin prick tests and potentially even a food challenge."

Sim advises those with any type of alcohol intolerance to avoid drinking altogether.

It's especially important to not drink alcohol if you have a genetic intolerance, as it will "increase your risk of alcohol-related organ damage, including some cancers and liver disease."

When it comes to allergies to any component of an alcoholic drink, you must never consume it. "It can be life-threatening," Sim says.

Disclaimer: The above does not constitute medical advice, if you are concerned about symptoms speak to a medical professional.

Originally published August 2022. Updated February 2026.

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