Alcohol intolerance is a physical reaction that occurs immediately or shortly after consuming alcoholic beverages. This condition is distinct from a true alcohol allergy, which is a rare, potentially severe immune system response to a specific ingredient within the drink. Intolerance results from the body’s difficulty in efficiently processing alcohol or one of its components. Symptoms commonly include facial flushing, nasal congestion, rapid heartbeat, and nausea, which are unpleasant but generally not life-threatening. The root causes are primarily metabolic, but they can also be traced to sensitivities to non-alcohol ingredients or interactions with certain medications.
Metabolic Dysfunction
The most common cause of alcohol intolerance is a genetic variation that interferes with the body’s ability to break down ethanol efficiently. The metabolism of alcohol is a two-step process that primarily takes place in the liver. First, the enzyme Alcohol Dehydrogenase (ADH) converts the ethanol into a highly toxic compound called acetaldehyde.
Acetaldehyde is responsible for many of the unpleasant physical effects associated with drinking, and its rapid removal is necessary. In the second step, the enzyme Aldehyde Dehydrogenase 2 (ALDH2) quickly converts this toxic acetaldehyde into harmless acetate, which the body can then excrete.
In many people, particularly those of East Asian descent, a genetic polymorphism exists in the gene that codes for the ALDH2 enzyme. This specific variation, often referred to as ALDH22, causes the enzyme to be significantly less effective or nearly inactive. Individuals with this genetic profile cannot process acetaldehyde quickly enough, leading to its rapid buildup in the bloodstream.
This toxic accumulation of acetaldehyde causes the characteristic symptoms of intolerance, sometimes called the “alcohol flush reaction.” The buildup triggers vasodilation, or the widening of blood vessels, which results in skin flushing, particularly in the face and neck. Other symptoms, such as headache, pounding heart (tachycardia), and nausea, are direct consequences of the body’s reaction to elevated acetaldehyde levels.
The severity of the reaction is determined by how many copies of the variant gene a person carries. Individuals who inherit one copy of the variant typically have reduced ALDH2 activity, while those with two copies may have virtually no functional enzyme.
Sensitivity to Beverage Components
While the metabolic pathway explains intolerance to ethanol itself, many people experience adverse reactions due to other compounds present in alcoholic drinks. These reactions are caused by naturally occurring or added ingredients, and the symptoms can vary depending on the type of beverage consumed.
One major category of triggers includes biogenic amines, such as histamine and tyramine, which are produced during the fermentation and aging processes. Red wine, beer, and certain fortified wines tend to contain higher levels of histamine compared to white wines or clear spirits. In sensitive individuals, the body may lack sufficient diamine oxidase (DAO), the enzyme needed to break down ingested histamine, leading to an excess that causes allergy-like symptoms.
The resulting histamine overload can lead to symptoms such as flushing, headache, nasal congestion, and asthma-like reactions. Another common trigger is sulfites, compounds used as preservatives to maintain freshness and prevent bacterial growth, especially in wine and beer. Sulfites can trigger respiratory issues, including wheezing and coughing, in people with sulfite sensitivity, particularly those with asthma.
Furthermore, reactions can be triggered by proteins from grains used in the production process. Beer and whiskey are made from grains like barley and wheat, and individuals with gluten sensitivity or celiac disease may react to residual grain proteins in these beverages. This highlights that a person may tolerate a distilled spirit but react negatively to a beer due to these specific, non-ethanol ingredients.
External Factors and Disease States
Beyond genetics and beverage ingredients, alcohol intolerance symptoms can be caused or intensified by external factors, most notably certain medications. Several common drugs interfere with the natural alcohol metabolism pathway, essentially mimicking the genetic ALDH2 deficiency. This interaction is a safety concern, as it causes a severe reaction known as a disulfiram-like effect.
Antibiotics like metronidazole and some antifungals, for example, work by inhibiting the ALDH enzyme, leading to a rapid and significant buildup of toxic acetaldehyde. When alcohol is consumed while taking these medications, the result is an intense reaction that includes severe nausea, vomiting, flushing, and a rapid or irregular heart rate.
In rare instances, an immediate and painful reaction to alcohol can signal an underlying medical condition. One such condition is Hodgkin’s lymphoma, where a small percentage of patients report pain in the affected lymph nodes immediately after drinking alcohol. The mechanism is not fully understood but is thought to involve the sudden vasodilation of blood vessels within the tumor or lymph node capsule.
A similar, though less common, reaction can be associated with carcinoid syndrome, which involves tumors that release vasoactive substances like serotonin. Experiencing severe pain or an unusually intense reaction to alcohol warrants a consultation with a healthcare professional to rule out these rare medical issues.