A formaldehyde releaser, formaldehyde donor or formaldehyde-releasing preservative is a chemical compound that slowly releases formaldehyde. Formaldehyde-releasers are added to prevent microbial growth and extend shelf life. The intent of these compounds is that they release formaldehyde at levels that suppress microbial growth but sufficiently low to not threaten humans. The use of these chemicals in cosmetics has elicited controversy.

Many compounds have been formulated as formaldehyde-releasers:

Some materials release formaldehyde unintentionally. These materials have also elicited considerable controversy, especially when these materials have household applications such as flooring. Examples:

They are found in fuels, cosmetics, toiletries, cleaning agents, adhesives, paints, lacquers, fertilizers, and metalworking fluids. They are found in lysing agent for cells for in vitro diagnostic reagents. Photo-chemicals and press room chemicals also contain these releasers.

Formaldehyde is dangerous to human health. In 2011, the US National Toxicology Program described formaldehyde as "known to be a human carcinogen".

The danger of formaldehyde is a major reason for the development of formaldehyde releasers which release formaldehyde slowly at lower levels.

Levels of 200–300 p.p.m. formaldehyde in cosmetic products can cause contact dermatitis in short-term use on normal skin.

A patch test study found that DMDM hydantoin in cosmetic products could increase the risk of cosmetic dermatitis.