Does green tea help against infections?

The evidence is strongest for influenza. A meta-analysis of eight studies involving more than three thousand participants shows that green tea catechins reduce the risk of influenza by around 33% in randomised trials, and by as much as approximately 48% in observational research. Both gargling and drinking or taking capsules appeared to work, which makes the effect more credible.

Against bacteria, green tea is impressive in the laboratory: catechins disrupt the bacterial cell, inhibit enzymes and deprive bacteria of the iron they need. The strongest activity is seen with specific catechins, of which EGCG is the best known. However, these are cell and animal experiments. Whether you would notice this effect in your own body during a real infection has not yet been demonstrated.

For HPV-related conditions, such as certain cervical lesions and genital warts, randomised studies do show a clinical effect of green tea catechins. This is separate from the influenza findings and specific to those conditions; it says nothing yet about other viral infections such as the common cold.

More broadly: green tea shows signs of antimicrobial properties across multiple types of research, but the strongest evidence applies only to influenza prevention. For most other infections, the evidence in humans is thin or absent.