Black Tea and Hair Growth: Three Lines of Research

Black tea has attracted hair-research interest for three different reasons: effects on androgen-related enzymes, blood-vessel signaling, and coat regrowth in mice. The topical mouse experiment is the most direct hair-growth finding; the other studies help explain why tea compounds are worth investigating.

These are promising laboratory and animal findings, not human hair-growth trials. They do not establish that black tea works like finasteride and minoxidil combined.

A fermented extract stimulated coat regrowth

In a 2013 experiment, researchers applied a 20% Chinese black-tea extract fermented with Aspergillus to shaved male mice daily for two weeks. The treated mice developed a significantly larger area of visible coat regrowth. Capsaicin strengthened the response, although it did not promote growth by itself.

The extract also interacted with estrogen receptor alpha in an assay, giving the researchers a possible explanation to pursue. The preparation was a specific fermented extract applied to skin, which makes it a different intervention from drinking tea.

Conceptual illustration of a topical tea-extract experiment with a mouse — Conceptual illustration, not a photograph from the study.

Theaflavins affected androgen-related targets

A 2004 study found that isolated theaflavin-3,3′-digallate and another polyphenol inhibited 5-alpha reductase in rat-liver preparations. This is the enzyme that makes DHT. The compounds also reduced androgen-receptor expression and other androgen-responsive signals in human prostate-cancer cells.

Our theaflavin review connects this mechanism research with the separate mouse DHT finding.

Tea also changed blood-vessel signaling

A 2009 study found that green and black Assam tea increased nitric-oxide-producing enzyme activity in cells from cow aortas and relaxed isolated rat arteries. Black-tea theaflavins and thearubigins contributed to the response. Read the vascular study.

This offers a reason to investigate circulation-related effects, although scalp blood flow was not measured. For the experiment that actually measured coat regrowth, continue to the fermented black-tea study.