How are LCT and allergy related?

The relationship between LCT (lactase gene) and allergies requires careful distinction. LCT encodes the lactase enzyme, which breaks down lactose. Variants in LCT (e.g., rs4988235) cause lactase non-persistence, leading to lactose intolerance—a digestive disorder, not an allergy. True milk allergy is an immune reaction to milk proteins (e.g., casein, whey) and is influenced by other genes. Some research explores indirect links: altered gut microbiota due to lactose malabsorption might affect immune regulation and slightly modulate risk for atopic conditions (e.g., hay fever, asthma). However, the evidence is weak and inconsistent. Most association studies find no direct causal effect of LCT variants on allergies. Clinically, LCT testing is used for lactose intolerance diagnosis, not allergy prediction. Consumers should understand that a positive LCT test does not indicate milk allergy, and vice versa. Marketing claims by some direct-to-consumer tests suggesting a link between LCT and allergies are not scientifically supported. For genuine allergy symptoms, an allergy test (IgE) is required.