Ingredient guide
Horsetail is a plant rich in silica, sold for hair, nails, and as a diuretic. A small trial supports a short-term diuretic effect. Evidence for hair and nails is weak, and there is a real thiamine-related safety caution.
Limited evidenceHorsetail is an ancient, fern-like plant, with the botanical name Equisetum arvense. Its claim to fame is silica, a mineral it accumulates in unusually large amounts. Silica is involved in connective tissue, which is why horsetail, and the related bamboo silica, are marketed for hair, skin, and nails, as well as for use as a diuretic.
Two ideas drive its use. The silica content is thought to support the building blocks of hair, nails, and connective tissue, though how much plant silica the body actually uses is unclear. Separately, horsetail contains compounds that promote urine production, which is the basis for its traditional use to reduce fluid retention.
The strongest human signal is for the diuretic effect. A randomised trial in healthy volunteers found that a horsetail extract increased urine output, comparable to a standard water tablet, without major changes in electrolytes. That is a genuine, if narrow, finding.
For hair and nails, the popular uses, good human trials are essentially missing, and the claims rest on the silica theory and tradition. There is also a real safety note. Some horsetail contains an enzyme that breaks down thiamine, vitamin B1, which matters for people already low in it. We grade the human evidence as limited, supported mainly for short-term diuretic use.
Horsetail is used as a tea or a standardised extract, often in hair and nail products alongside bamboo silica. Keep use short rather than continuous, and look for products labelled free of the thiamine-degrading enzyme. If you take diuretic medicine, have kidney or heart problems, or drink heavily, check with a healthcare provider first.
There is no established dose. Traditional use ranges from teas to leaf extracts and silica-standardised products. Some hair and nail products combine it with bamboo silica. Ask your healthcare provider before regular use, especially if you take diuretic medicine or drink heavily.
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A randomised trial found a horsetail extract increased urine output comparably to a standard water tablet, so there is real support for short-term diuretic use.
Short-term use is usually well tolerated. The main caution is that some horsetail breaks down thiamine (B1), so heavy drinkers and those low in B1 should avoid it.
Bamboo extract is another very high silica source, often paired with or used instead of horsetail in hair and nail products for the same silica rationale.