US FDA warns against “black henna” as scientists develop safe alternative

The US Food and Drug Administration (FDA) has renewed its warning about temporary tattoos and “black henna” body art, after receiving multiple reports of allergic reactions and chemical burns linked to these products.

The agency emphasizes that henna is only approved for use as a hair dye, not for direct application to the skin.

Moreover, many “black henna” products illegally contain p-phenylenediamine (PPD), a chemical known to cause severe skin reactions.

The agency’s warnings come as consumer interest in natural colorants continues to grow. The demand has prompted industry innovators to explore safer, plant-based formulations that meet safety and performance standards.

One such innovation is outlined in a new study by researchers at Henkel and the University of Hamburg, Germany. Their research proposes an enzyme-activated henna system that stabilizes natural dye precursors for hair care applications.

“Black henna” hazards

According to the FDA, many temporary tattoo products, especially those marketed as “black henna” or “blue henna,” contain unapproved color additives. These additives can cause dangerous skin reactions.

The additive most often responsible is PPD, a coal-tar-derived dye that, according to the FDA, is only allowed in hair products and not in cosmetics applied to the skin. The agency warns that PPD exposure can trigger blistering, scarring, or lifelong sensitivity, even from a single application.

“Black henna” mixtures often blend natural henna with PPD to create a darker, longer-lasting stain. However, the FDA notes the practice makes such products adulterated and illegal under US law.

Even pure henna, when marketed for body art, falls outside FDA approval, as it is considered an unapproved use of a color additive.

The agency stresses that products lacking full ingredient labeling or falsely claiming to be “FDA-approved” are misbranded and subject to import alerts.

Many “black henna” temporary-tattoo products illegally contain PPD, a coal-tar-derived dye known to cause severe skin reactions.The FDA urges consumers to be cautious, perform patch tests, and report adverse reactions to the agency. As enforcement varies by state, not all tattoo artists or vendors follow safety regulations.

Controlled innovation

In contrast to unsafe “black henna” products, scientists at Henkel and the University of Hamburg have developed a two-component, enzyme-catalyzed henna system that may redefine the use of Lawsonia inermis in cosmetics.

The research, published in the International Journal of Cosmetic Science, describes how hennosides can be stabilized and activated using the enzyme β-glucosidase just before application.

Hennosides are natural, water-soluble precursors of the dye molecule lawsone, derived from the henna plant’s natural dye.

Unlike traditional henna pastes, which are unstable and degrade over time, the enzyme-activated gel remains stable for over eight weeks. The researchers say it delivers consistent color results and avoids premature dye release and microbial contamination.

The tested henna’s controlled release mechanism keeps lawsone concentrations below the 0.35% safety threshold defined by EU regulators, thereby making the formulation effective and compliant.

By separating the dye precursor (hennosides) from the activating enzyme until use, the researchers believe the innovation could lead to safe, standardized, and fully regulated henna-based hair colorants.