Formaldehyde is a colorless gas with a strong, distinct odor. It is used in various industries, including some cosmetic and hair care products, as a preservative, disinfectant, or as an ingredient in certain hair straightening treatments. Some formaldehyde releasing preservatives are often found in horse grooming products, they include:  polyquaternium-7, polyquaternium-10, quaternium-15, diazolidinyl urea, DMDM hydantoin, bronopol, and imidazolidinyl urea. 

Formaldehyde and formaldehyde-releasing compounds can have potential impacts on skin, hair, and the environment. Here's an overview:

Skin and hair effects: Formaldehyde can be a skin and respiratory irritant, especially when used in high concentrations or in products that release formaldehyde gas. Direct contact with formaldehyde can cause skin irritation, redness, itching, and allergic reactions. It can also lead to scalp irritation, dryness, and potential hair breakage.

Sensitization and allergies: Prolonged exposure to formaldehyde can cause sensitization, leading to an increased risk of developing allergies. Some individuals may develop allergic reactions, such as contact dermatitis or asthma symptoms, when exposed to formaldehyde or formaldehyde-releasing compounds.

Carcinogenic potential: Formaldehyde is classified as a known human carcinogen by the International Agency for Research on Cancer (IARC). Prolonged exposure to high levels of formaldehyde has been associated with an increased risk of certain cancers, including nasal and throat cancers.

Environmental impact: Formaldehyde can be released into the environment through various sources, including the use and disposal of products containing formaldehyde. It can contribute to air pollution and may have adverse effects on ecosystems when released into water bodies.

To address these concerns, regulatory authorities in many countries have established guidelines and regulations to limit the use of formaldehyde in cosmetic and personal care products. Additionally, many brands offer formaldehyde-free or low-formaldehyde formulations, especially in hair care products and treatments.