Formaldehyde enters the environment due to human activity but also occurs in nature. Formaldehyde and formalin have various industrial uses. In histopathology, formalin is used for fixing tissues to preserve cells and tissue architecture, due to its ability to cross-link amino acids. For this reason, it is also used in embalming.

Health effects of formalin

Various health effects are attributable to formalin. The International Agency for Research on Cancer (part of the WHO) classifies formaldehyde as a Group I carcinogen (also in this group are asbestos and benzene). The EPA (USA) considers formaldehyde a probable human carcinogen (group B1).

Shorter term issues caused by formaldehyde exposure include eye, nose and throat irritation. Long-term inhalation may trigger IgE-meditated nasal allergy in atopic people. There have been reports of dermatitis and skin sensitisation amongst histotechnologists after exposure to formalin. If ingested, formaldehyde causes corrosion and ulceration of the oral, oesophageal and gastric mucosa. Correlation has been found between formaldehyde exposure and reproductive and developmental toxicity in humans but further research is required to determine the mechanism and significance of these effects.

For further information:

American Chemistry Council: Chemical Safety Facts

EPA fact sheet

U.S. Environmental Protection Agency. Health and Environmental Effects Profile for Formaldehyde. EPA/600/x-85/362. Environmental Criteria and Assessment Office, Office of Health and Environmental Assessment, Office of Research and Development, Cincinnati, OH. 1988

Dapson JC, Dapson RW. Hazardous Materials in the Histopathology Laboratory: Regulation, Risks, Handling and Disposal. 4th ed. Battle Creek, MI: Anatech LTD; 2005.

Dimenstein, I.B., 2009. A pragmatic approach to formalin safety in anatomical pathology. Laboratory Medicine, 40(12), pp.740-746. Available here:

Duong, A., Steinmaus, C., McHale, C.M., Vaughan, C.P. and Zhang, L., 2011. Reproductive and developmental toxicity of formaldehyde: a systematic review. Mutation Research/Reviews in Mutation Research, 728(3), pp.118-138.

Wilhelmsson B, Holmstrom M. Positive formaldehyde-RAST after prolonged formaldehyde exposure by inhalation. Lancet. 1987;2:164.

Environmental impact of formalin

Formaldehyde biodegrades readily in air, water and soil under both aerobic and anaerobic conditions. In the air, formaldehyde breaks down in sunlight to form carbon monoxide and formic acids, a component of acid rain. It is not commonly found in drinking water and is found in limited quantities in foods such as cheeses and grains where it occurs naturally and is also added to kill pathogens. Formaldehyde is not bioaccumulative and does not persist in the environment, but its continuous release and formation result in long-term exposure near sources of release and formation.

Environmental toxicity data are available for a wide range of terrestrial and aquatic organisms. Based on the maximum concentrations of formaldehyde measured in air, surface water, effluents, and groundwater in the sample exposure scenario from the source country in one Canadian-based study, and on the estimated no-effects values derived from experimental data for terrestrial and aquatic biota, formaldehyde is not likely to cause adverse effects on terrestrial or aquatic organisms.

For further information:

Massachusetts Chemical Fact Sheet

Disposal of formalin

Formalin is a hazardous waste and must be disposed of responsibly. General information regarding hazardous waste disposal in the UK is provided by the Environmental Agency.

Formalin may also be neutralised prior to disposal, converting it to non-toxic products.

Chemical waste disposal companies collect chemicals including formalin and dispose of them in a safe manner.

Formalin can also be recycled via distillation or filtration and subsequently reused, saving materials and money.

For further information re general waste disposal:

Gov.UK – Dispose of Business or Commercial Waste

Gov.UK – Hazardous waste

For further information re formalin disposal and recycling:

National Society for Histotechnology: Formalin Disposal

Prakash R, Carmichael ST. Evaluation of two eco-friendly neutralizers for a spectrum of tissue fixatives for biomedical applications. Future Sci OA. 2018;4(8):FSO329. Published 2018 Aug 10. doi:10.4155/fsoa-2018-0035

Formalin recycling in health care labs: Fact Sheet, Univeristy of Minnesota

Alternatives to formalin

Natural and commercial alternatives to formalin are available. Natural fixatives that have been subjected to research include honey and other natural sweeteners (e.g. sugar, jaggery and khandasari). Alcohol-based fixatives have been compared to formalin in various studies. There are “green” alternatives to formalin commercially-available.

Alcohol-based fixatives, which pose less safety concerns than formalin, are an alternative option as fixatives. Several studies have shown alcohol-based fixation is faster than when formalin is used and yields comparable results in terms of tissue morphology and preservation of epitopes for immunohistochemistry. Read more here…

An interesting new development is the use of vacuum packaging of samples to decrease the amounts of formalin used.

For further information re formalin alternatives in general:

National Society for Histotechnology: Alternatives to formalin.

For further information re natural alternatives to formalin:

Al-Maaini, R. and Bryant, P., 2006. The effectiveness of honey as a substitute for formalin in the histological fixation of tissue. Journal of Histotechnology, 29(3), pp.173-176.

Özkan, N., Şalva, E., Cakalağaoğlu, F. and Tüzüner, B., 2012. Honey as a substitute for formalin?. Biotechnic & Histochemistry, 87(2), pp.148-153.

Sabarinath, B., Sivapathasundharam, B. and Sathyakumar, M., 2014. Fixative properties of honey in comparison with formalin. Journal of Histotechnology, 37(1), pp.21-25.

Patil, S., Premalatha, B.R., Rao, R.S. and Ganavi, B.S., 2013. Revelation in the field of tissue preservation–A preliminary study on natural formalin substitutes. Journal of international oral health: JIOH, 5(1), p.31.

Patil, S., Rao, R.S., Ganavi, B.S. and Majumdar, B., 2015. Natural sweeteners as fixatives in histopathology: A longitudinal study. Journal of natural science, biology, and medicine, 6(1), p.67.

Chittemsetti, S., Nallamala, S., Sravya, T., Guttikonda, V.R., Manchikatla, P.K. and Kondamari, S., 2018. Natural substitutes for formalin: A boon to histopathology!!. Journal of oral and maxillofacial pathology: JOMFP, 22(1), p.143.

For further information re alcohol-based alternatives to formalin:

Bostwick, D.G., al Annouf, N.A.B.I.L. and Choi, C., 1994. Establishment of the formalin-free surgical pathology laboratory. Utility of an alcohol-based fixative. Archives of pathology & laboratory medicine, 118(3), pp.298-302.

Chung, J.Y., Song, J.S., Ylaya, K., Sears, J.D., Choi, L., Cho, H., Rosenberg, A.Z. and Hewitt, S.M., 2018. Histomorphological and molecular assessments of the fixation times comparing formalin and ethanol-based fixatives. Journal of Histochemistry & Cytochemistry, 66(2), pp.121-135.

Haque, Z., Rahman, M.A., Khan, M.Z.I., Hussan, M.T., Alam, M.M., HAQUE, Z., RAHMAN, M., KHAN, M., HUSSAN, M. and ALAM, M., 2020. Alcohol-Based Fixatives can Better Preserve Tissue Morphology than Formalin. Int. j. morphol, 38(5), pp.1371-1375.

Hostein, I., Stock, N., Soubeyran, I., Marty, M., De Mascarel, I., Bui, M., Geneste, G., Petersen, M.C., Coindre, J.M. and MacGrogan, G., 2011. Nucleic acid quality preservation by an alcohol-based fixative: comparison with frozen tumors in a routine pathology setting. Diagnostic Molecular Pathology, 20(1), pp.52-62.

Milcheva, R., Janega, P., Celec, P., Russev, R. and Babál, P., 2013. Alcohol based fixatives provide excellent tissue morphology, protein immunoreactivity and RNA integrity in paraffin embedded tissue specimens. Acta histochemica, 115(3), pp.279-289.

Panzacchi, S., Gnudi, F., Mandrioli, D., Montella, R., Strollo, V., Merrick, B.A., Belpoggi, F. and Tibaldi, E., 2019. Effects of short and long-term alcohol-based fixation on Sprague-Dawley rat tissue morphology, protein and nucleic acid preservation. Acta histochemica, 121(6), pp.750-760.

Perry, C., Chung, J.Y., Ylaya, K., Choi, C.H., Simpson, A., Matsumoto, K.T., Smith, W.A. and Hewitt, S.M., 2016. A buffered alcohol-based fixative for histomorphologic and molecular applications. Journal of Histochemistry & Cytochemistry, 64(7), pp.425-440.

Rahman, M.A., Sultana, N., Ayman, U., Bhakta, S., Afrose, M., Afrin, M. and Haque, Z., 2021. Alcoholic fixation over formalin fixation: A new, safer option for morphologic and molecular analysis of tissues. Saudi Journal of Biological Sciences.

Warmington, A.R., Wilkinson, J.M. and Riley, C.B., 2000. Evaluation of ethanol-based fixatives as a substitute for formalin in diagnostic clinical laboratories. Journal of Histotechnology, 23(4), pp.299-308.

Zanini, C., Gerbaudo, E., Ercole, E., Vendramin, A. and Forni, M., 2012. Evaluation of two commercial and three home-made fixatives for the substitution of formalin: a formaldehyde–free laboratory is possible. Environmental Health, 11(1), pp.1-14.

For further information re vacuum-packing of samples:

Annaratone, L., Marchiò, C. and Sapino, A., 2019. Tissues under-vacuum to overcome suboptimal preservation. New biotechnology, 52, pp.104-109.

Mastraci L, et al (2019) Coping with formalin banning in pathology: under vacuum long-term tissue storage with no added formalin Histochemistry and Cell Biology, 151, 501-511 The paper is available here.

Zarbo, R.J., 2015. Histologic validation of vacuum sealed, formalin-free tissue preservation, and transport system. In Pre-Analytics of Pathological Specimens in Oncology (pp. 15-26). Springer, Cham.

Case example: Heartlands Hospital, part of University Hospitals Birmingham NHS Foundation Trust (UHB), the lead organisation for the West Midlands Genomic Medicine Centre (WMGMC) is using vacuum packing read about it here