Why is there aluminium in deoderant

The short version: aluminum compounds are in antiperspirants to block sweat pores, not to deodorize. The question is whether that daily dermal exposure adds up to a body burden worth worrying about.

Aluminum salts (usually aluminum chlorohydrate or aluminum zirconium) work by forming a gel plug inside the sweat duct. That physically stops sweat from reaching the skin surface. It is a mechanical effect, not a chemical neutralization of odor. The FDA classifies these as over-the-counter antiperspirant drugs, not cosmetics, because they alter a body function.

The evidence on absorption is thin for the general question you asked. What we have comes from studies on other routes. Oral aluminum absorption is low—about 0.01% to 0.5% depending on what it is eaten with [3]. Citric acid sharply increases absorption [5, 9]. Dermal absorption through intact skin is less studied, but the underarm skin is thin, often shaved (which removes the barrier), and the product stays on for hours. A 2004 review of aluminum-26 tracer studies in humans found that once absorbed, aluminum distributes to bone (about 54% of total body burden) and brain, with a long-term half-life in bone of about 1,727 days [3]. That means it accumulates.

The rat studies in the evidence show that aluminum citrate causes brain levels roughly double control and bone levels roughly 50 times control after oral dosing [5]. Those are rat numbers, not human, but the mechanism—aluminum crossing the blood-brain barrier via transferrin receptors—is the same. The human tracer data confirm that a fraction of every absorbed dose stays in the body for years [3].

What is missing is a direct study comparing antiperspirant users to non-users for tissue aluminum levels or long-term health outcomes. The evidence we have is about oral and injected aluminum, not dermal. That gap is the problem. The burden of proof is on the product, and the product's safety case relies on the assumption that skin blocks aluminum completely. The evidence does not support that assumption.

My call: the evidence does not prove that antiperspirant aluminum is safe at the doses accumulated over a lifetime, because the dermal absorption studies were never done to the standard that would settle it. Confidence: moderate—the mechanism is plausible, the human tracer data show long retention, and the missing study is the most informative one.