are used as biocides in personal care products such as cosmetics. although present at levels not normally considered harmful, they are known to cause allergic contact dermatitis in certain sensitised individuals. aquarists use formaldehyde as a treatment for the parasites ichthyophthirius multifiliis and cryptocaryon irritans. formaldehyde is also approved for use in the manufacture of animal feeds in the us. it is an antimicrobial agent used to maintain complete animal feeds or feed ingredients salmonella negative for up to 21 days. tissue fixative and embalming agent injecting a giant squid specimen with formalin for preservation formaldehyde preserves or fixes tissue or cells. the process involves cross-linking of primary amino groups. the european union has banned the use of formaldehyde as a biocide (including embalming) under the biocidal products directive (98/8/ec) due to its carcinogenic properties. countries with a strong tradition of embalming corpses, such as ireland and other colder-weather countries, have raised concerns. despite reports to the contrary, no decision on the inclusion of formaldehyde on annex i of the biocidal products directive for product-type 22 (embalming and taxidermist fluids) had been made as of september 2009. formaldehyde-based crosslinking is exploited in chip-on-chip or chip-sequencing genomics experiments, where dna-binding proteins are cross-linked to their cognate binding sites on the chromosome and analyzed to determine what genes are regulated by the proteins. formaldehyde is also used as a denaturing agent in rna gel electrophoresis, preventing rna from forming secondary structures. a solution of 4% formaldehyde fixes pathology tissue specimens at about one mm per hour at room temperature. drug testing formaldehyde and an 18 m (concentrated) sulfuric acid makes marquis reagent—which can identify alkaloids and other compounds. photography in photography, formaldehyde is used in low concentrations for the process c-41 (color negative film) stabilizer in the final wash step, as well as in the process e-6 pre-bleach step, to make it unnecessary in the final wash. safety in view of its widespread use, toxicity, and volatility, formaldehyde poses a significant danger to human health. in 2011, the us national toxicology program described formaldehyde as "known to be a human carcinogen". however, concerns are associated with chronic (long term) exposure by inhalation as may happen from thermal or chemical decomposition of formaldehyde-based resins and the production of formaldehyde resulting from the combustion of a variety of organic compounds (for example, exhaust gases). as formaldehyde resins are used in many construction materials, it is one of the more common indoor air pollutants. at concentrations above 0.1 ppm in air, formaldehyde can irritate the eyes and mucous membranes. formaldehyde inhaled at this concentration may cause headaches, a burning sensation in the throat, and difficulty breathing, and can trigger or aggravate asthma symptoms. the cdc considers formaldehyde as a systemic poison. formaldehyde poisoning can cause permanent changes in the nervous system's functions. a 1988 canadian study of houses with urea-formaldehyde foam insulation found that formaldehyde levels as low as 0.046 ppm were positively correlated with eye and nasal irritation. a 2009 review of studies has shown a strong association between exposure to formaldehyde and the development of childhood asthma. a theory was proposed for the carcinogenesis of formaldehyde in 1978. in 1987 the united states environmental protection agency (epa) classified it as a probable human carcinogen, and after more studies the who international agency for research on cancer (iarc) in 1995 also classified it as a probable human carcinogen. further information and evaluation of all known data led the iarc to reclassify formaldehyde as a known human carcinogen associated with nasal sinus cancer and nasopharyngeal cancer. studies in 2009 and 2010 have also shown a positive correlation between exposure to formaldehyde and the development of leukemia, particularly myeloid leukemia. nasopharyngeal and sinonasal cancers are relatively rare, with a combined annual incidence in the united states of < 4,000 cases. about 30,000 cases of myeloid leukemia occur in the united states each year. some evidence suggests that workplace exposure to formaldehyde contributes to sinonasal cancers. professionals exposed to formaldehyde in their occupation, such as funeral industry workers and embalmers, showed an increased risk of leukemia and brain cancer compared with the general population. other factors are important in determining individual risk for the development of leukemia or nasopharyngeal cancer. in yeast, formaldehyde is found to perturb pathways for dna repair and cell cycle. in the residential environment, formaldehyde exposure comes from a number of routes; formaldehyde can be emitted by treated wood products, such as plywood or particle board, but it is produced by paints, varnishes, floor finishes, and cigarette smoking as well. in july 2016, the u.s. epa released a prepublication version of its final rule on formaldehyde emission standards for composite wood products. these new rules impact manufacturers, importers, distributors, and retailers of products containing composite wood, including fiberboard, particleboard, and various laminated products, who must comply with more stringent record-keeping and labeling requirements. the u.s. epa allows no more than 0.016 ppm formaldehyde in the air in new buildings constructed for that agency. a u.s. environmental protection agency study found a new home measured 0.076 ppm when brand new and 0.045 ppm after 30 days. the federal emergency management agency (fema) has also announced limits on the formaldehyde levels in trailers purchased by that agency. the epa recommends the use of "exterior-grade" pressed-wood products with phenol instead of urea resin to limit formaldehyde exposure, since pressed-wood products containing formaldehyde resins are often a significant source of formaldehyde in homes. patch test for most people, irritation from formaldehyde is temporary and reversible, although formaldehyde can cause allergies and is part of the standard patch test series. in 2005–06, it was the seventh-most-prevalent allergen in patch tests (9.0%). people with formaldehyde allergy are advised to avoid formaldehyde releasers as well (e.g., quaternium-15, imidazolidinyl urea, and diazolidinyl urea). people who suffer allergic reactions to formaldehyde tend to display lesions on the skin in the areas that have had direct contact with the substance, such as the neck or thighs (often due to formaldehyde released from permanent press finished clothing) or dermatitis on the face (typically from cosmetics). formaldehyde has been banned in cosmetics in both sweden and japan. the eyes are most sensitive to formaldehyde exposure: the lowest level at which many people can begin to smell formaldehyde ranges between 0.05 and 1 ppm. the maximum concentration value at the workplace is 0.3 ppm. in controlled chamber studies, individuals begin to sense eye irritation at about 0.5 ppm; 5 to 20 percent report eye irritation at 0.5 to 1 ppm; and greater certainty for sensory irritation occurred at 1 ppm and above. while some agencies have used a level as low as 0.1 ppm as a threshold for irritation, the expert panel found that a level of 0.3 ppm would protect against nearly all irritation. in fact, the expert panel found that a level of 1.0 ppm would avoid eye irritation—the most sensitive endpoint—in 75–95% of all people exposed. some air purifiers include filtering technology that is supposed to lower indoor formaldehyde concentration. formaldehyde levels in building environments are affected by a number of factors. these include the potency of formaldehyde-emitting products present, the ratio of the surface area of emitting materials to volume of space, environmental factors, product age, interactions with other materials, and ventilation condition. formaldehyde emits from a variety of construction materials, furnishings, and consumer products. the three products that emit the highest concentrations are medium density fiberboard, hardwood plywood, and particle board. environmental factors such as temperature and relative humidity can elevate levels because formaldehyde has a high vapor pressure. formaldehyde levels from building materials are the highest when a building first opens because materials would have less time to off-gas. formaldehyde levels decrease over time as the sources suppress. formaldehyde levels in air can be sampled and tested in several ways, including impinger, treated sorbent, and passive monitors. the national institute for occupational safety and health (niosh) has measurement methods numbered 2016, 2541, 3500, and 3800. studies on the interactions between formaldehyde and proteins at the molecular level have been reported on the effects of the body's carrier protein, serum albumin. the binding of formaldehyde loosens the skeletal structure of albumin and causes exposure of aromatic ring amino acids in the internal hydrophobic region. symptoms may affect personal awareness, making one feel tired or fatigued. formaldehyde inhalation has also shown to cause oxidative stress and inflammation in animals. mice studied over an exposure to a high dose of formaldehyde (3ppm), showed increased no−3 levels in plasma. this result suggests that fa inhalation either decreased no production or increased no scavenging, which may be an anti-stress mechanism in the body. formaldehyde inhalation changes the sensitivity of immune system, which influences oxidative stress. in june 2011, the twelfth edition of the national toxicology program (ntp) report on carcinogens (roc) changed the listing status of formaldehyde from "reasonably anticipated to be a human carcinogen" to "known to be a human carcinogen." concurrently, a national academy of sciences (nas) committee was convened and issued an independent review of the draft u.s. epa iris assessment of formaldehyde, providing a comprehensive health effects assessment and quantitative estimates of human risks of adverse effects. formaldehyde occurs naturally, and is "an essential intermediate in cellular metabolism in mammals and humans." according to the american chemistry council, "formaldehyde is found in every living system—from plants to animals to humans. it metabolizes quickly in the body, breaks down rapidly, is not persistent and does not accumulate in the body." international bans several web articles claim that formaldehyde has been banned from manufacture or import into the european union (eu) under reach (registration, evaluation, authorization, and restriction of chemical substances) legislation. that is a misconception, as formaldehyde is not listed in the annex i of regulation (ec) no 689/2008 (export and import of dangerous chemicals regulation), nor on a priority list for risk assessment. however, formaldehyde is banned from use in certain applications (preservatives for liquid-cooling and processing systems, slimicides, metalworking-fluid preservatives, and antifouling products) under the biocidal products directive. in the eu, the maximum allowed concentration of formaldehyde in finished products is 0.2%, and any product that exceeds 0.05% has to include a warning that the product contains formaldehyde. in the united states, congress passed a bill july 7, 2010 regarding the use of formaldehyde in hardwood plywood, particle board, and medium density fiberboard. the bill limited the allowable amount of formaldehyde emissions from these wood products to 0.09 ppm, and required companies to meet this standard by january 2013. the final u.s. epa rule specified maximum emissions of "0.05 ppm formaldehyde for hardwood plywood, 0.09 ppm formaldehyde for particleboard, 0.11 ppm formaldehyde for medium-density fiberboard, and 0.13 ppm formaldehyde for thin medium-density fiberboard." formaldehyde was declared a toxic substance by the 1999 canadian environmental protection act. external mediaaudio "episode 202: where have all the fema trailers gone? tracing toxicity from bust to boom", distillations, september 2, 2015, science history institutevideo where have all the trailers gone?, video by mariel carr (videographer) & nick shapiro (researcher), 2015, science history institute contaminant in food scandals have broken in both the 2005 indonesia food scare and 2007 vietnam food scare regarding the addition of formaldehyde to foods to extend shelf life. in 2011, after a four-year absence, indonesian authorities found foods with formaldehyde being sold in markets in a number of regions across the country. in august 2011, at least at two carrefour supermarkets, the central jakarta livestock and fishery sub-department found cendol containing 10 parts per million of formaldehyde. in 2014, the owner of two noodle factories in bogor, indonesia, was arrested for using formaldehyde in noodles. 50 kg of formaldehyde was confiscated. foods known to be contaminated included noodles, salted fish, and tofu. chicken and beer were also rumored to be contaminated. in some places, such as china, manufacturers still use formaldehyde illegally as a preservative in foods, which exposes people to formaldehyde ingestion. in humans, the ingestion of formaldehyde has been shown to cause vomiting, abdominal pain, dizziness, and in extreme cases can cause death. testing for formaldehyde is by blood and/or urine by gas chromatography-mass spectrometry. other methods include infrared detection, gas detector tubes, etc., of which high-performance liquid chromatography is the most sensitive. in the early 1900s, it was frequently added by us milk plants to