Metalworking fluid health hazards reach workers through skin contact and inhaled mist: the UK Health and Safety Executive lists dermatitis, occupational asthma, hypersensitivity pneumonitis, bronchitis and upper airway irritation, and NIOSH counts about 1.2 million potentially exposed US workers. Which part of the fluid causes which harm, and how is it kept down?
The fluids in question are metalworking fluids (MWF), the cutting, grinding and forming fluids that cool and lubricate the cut, so cutting fluid health hazards and coolant health hazards name the same risks.
NIOSH (1998, as cited by OSHA) puts 14 to 67 % of exposed workers at risk of dermatitis, and poorly refined mineral oils used before 1985 are linked to six cancer sites. OSHA sets no limit specific to metalworking fluids; NIOSH recommends 0.4 mg/m³ thoracic, and control rests on enclosure, ventilation, weekly fluid checks and gloves.
Standards, regulations and exposure limits are checked against their issuing bodies, product values against the named data sheet, and every figure carries its source and date; see our methodology and fact-checking.
What Are the Health Hazards of Metalworking Fluids?#
The safety hazards associated with cutting fluid are skin disease, respiratory disease and, for older poorly refined mineral oils, cancer. The UK Health and Safety Executive lists dermatitis, occupational asthma, hypersensitivity pneumonitis, bronchitis and upper airway irritation ("About metalworking fluids", updated 4 December 2024).
The hazard set differs by fluid because four sources feed it: the base oil, the additives, contaminants picked up in use and microbes in the sump. Each hazard of metalworking fluids and their additives traces back to one of them, and this reference on metalworking fluids and their additives follows all four.
Who is exposed to metalworking fluids?#
About 1.2 million US workers are potentially exposed to metalworking fluids, according to the NIOSH topic page last reviewed in August 2013. Germany uses about 50,000 t (about 55,000 short tons) of metalworking fluids a year (IFA), and UK shop floors know the same fluids as "suds", "coolants", "slurry" or "soap" (HSE).
How Does Exposure to Metalworking Fluids Happen?#
Metalworking fluid exposure happens by three routes: skin contact, inhalation of mist and ingestion. The UK COSHH Regulations 2002 (ACOP L5) require each route to be prevented where reasonably practicable or adequately controlled.
Skin contact comes from handling wet parts and cleaning sumps by hand. Mist comes from the cutting zone, from opening machine doors before the mist settles at cycle end, and from compressed-air blow-off; HSE guidance MW1 places the breathing zone 20 to 30 cm (8 to 12 in) from nose and mouth.
Health Effects of Metalworking Fluids on Skin, Lungs and Cancer Risk#
Metalworking fluids health effects fall into four areas: the skin, the airways, the mist that carries fluid into the lungs, and cancer.
Skin contact and the dermatitis risk#
Skin contact causes irritant and allergic contact dermatitis, and NIOSH (1998, as cited by OSHA) puts 14 to 67 % of exposed workers at risk. Allergic dermatitis follows from sensitizers in the concentrate, such as monoethanolamine, colophonium and formaldehyde releasers. Straight oils are linked to folliculitis, oil acne and keratoses (NIOSH 98-116, 1998).
Airways, occupational asthma and hypersensitivity pneumonitis#
Inhaled fluid affects the airways through occupational asthma and hypersensitivity pneumonitis, with NIOSH finding the asthma evidence strongest for synthetic MWF aerosol (NIOSH 98-116). A NIOSH workshop report (Kreiss and Cox-Ganser, 1997) describes 8 hypersensitivity pneumonitis clusters in US auto plants using water-based fluids, most cases below 0.5 mg/m³. Metalworking fluids are now the predominant cause of occupational hypersensitivity pneumonitis in the UK (peer-reviewed review, PubMed 33394701).
Mist as the airborne carrier of fluid#
Mist is the airborne form of the fluid, and it carries oil, additives and microbes into the breathing zone. High-pressure through-tool coolant at 55 bar (800 psi) raised mist concentration by about 200 % in one study, with the droplet size distribution unchanged (PubMed 10782200). Machine enclosures are the most effective engineering control for mist (OECD ESD No. 28, 2011).
Do metalworking fluids cause cancer?#
Yes for older fluids: metalworking fluids made from poorly refined mineral oils before 1985 are linked to cancers of the larynx, rectum, pancreas, skin, scrotum and bladder (OSHA). IARC classifies untreated or mildly treated mineral oils in Group 1 (Volume 100F, 2012) but highly refined mineral oils in Group 3 (Supplement 7, 1987). California lists "mineral oils, untreated and mildly treated" under Proposition 65 as causing cancer since 27 February 1987 (OEHHA).
A NIOSH risk model (Park, 2018, PubMed 29327473) estimates an attributable lifetime cancer risk of 3.7 % (3.1 % excluding female cancers) at 0.1 mg/m³ for 45 years of work, for cancers of the larynx, esophagus, brain, female breast and cervix. N-nitrosodiethanolamine and formaldehyde add carcinogens to fluids in use, as the substance table below shows.
Complete Table of Metalworking Fluid Health and Safety Topics#
The table lists all six health and safety topics this reference covers in depth, with the hazard each one addresses, one key figure with its source and the page that explains it.
| # | Topic | Hazard covered | Key figure and source | Who it is for |
|---|---|---|---|---|
| 1 | coolant dermatitis | irritant and allergic contact dermatitis from fluid on the skin | 14 to 67 % of exposed workers at risk (NIOSH 1998, as cited by OSHA) | EHS staff, supervisors, operators |
| 2 | respiratory disease from metalworking fluids | occupational asthma and hypersensitivity pneumonitis | 8 US clusters of hypersensitivity pneumonitis, most cases below 0.5 mg/m³ (Kreiss and Cox-Ganser, NIOSH workshop, 1997) | occupational-health staff, EHS staff |
| 3 | metalworking fluid mist | how mist forms, is measured and is controlled | through-tool coolant at 55 bar (800 psi) raised mist concentration by about 200 % in one study (PubMed 10782200) | engineers, EHS staff |
| 4 | metalworking fluid exposure limits | NIOSH, OSHA, ACGIH, HSE and EU values by jurisdiction | NIOSH REL 0.4 mg/m³ thoracic (about 0.5 mg/m³ total), TWA up to 10 h/day in a 40-h week (NIOSH 98-102, January 1998) | EHS staff, occupational hygienists |
| 5 | nitrosamines in metalworking fluids | NDELA from secondary amines and nitrite | NDELA: CLP Annex VI 612-090-00-4, Carc. 1B H350 (original Annex VI list) | formulators, fluid managers |
| 6 | formaldehyde-releasing biocides | formaldehyde released by biocides in the sump | formaldehyde released from MBO (612-290-00-1) and HPT (612-291-00-7): Carc. 1B H350, Muta. 2 H341 (ATP10, since 1 December 2018) | formulators, fluid managers, EHS staff |
Cancer risk has no separate page; the cancer section above covers it.
Which Additives and Contaminants Carry Classified Hazards?#
This reference lists eleven substances in metalworking fluids with classified health hazards, from boric acid (index 005-007-00-2, Repr. 1B H360FD) to NDELA (index 612-090-00-4, Carc. 1B H350). The table compares each substance's role, its CLP Annex VI line (never one safety data sheet) and its other health listings.
| Substance (CAS) | Role in the fluid | CLP Annex VI line (index, ATP, date) | Other health listing |
|---|---|---|---|
| mineral oils, untreated or mildly treated (base oils) | carrier fluid | see the product SDS | IARC Group 1 (Vol. 100F, 2012); highly refined oils Group 3 (Suppl. 7, 1987); California Prop 65 "mineral oils, untreated and mildly treated", cancer, 1987-02-27 |
| monoethanolamine, MEA (141-43-5) | alkanolamine, pH and reserve alkalinity | 603-030-00-8 (original Annex VI list): Acute Tox. 4 H302, H312, H332; Skin Corr. 1B H314; SCL STOT SE 3 H335 at 5 % or more | most frequent MWF allergen, 12.6 % positive (IVDK 2010 to 2018); not a CLP sensitizer |
| diethanolamine, DEA (111-42-2) | alkanolamine (secondary amine) | 603-071-00-1 (original Annex VI list): Acute Tox. 4 H302, STOT RE 2 H373, Skin Irrit. 2 H315, Eye Dam. 1 H318 | IARC Group 2B; Prop 65 cancer, 2012-06-22; NDELA precursor |
| boric acid (10043-35-3) | corrosion inhibitor, biostatic | 005-007-00-2: Repr. 1B H360FD; current entry ATP20 (Reg. (EU) 2023/1435) with Note 11, in application since 2025-02-01 | REACH Candidate List since 2010-06-18 |
| N-nitrosodiethanolamine, NDELA (1116-54-7) | contaminant formed in use | 612-090-00-4 (original Annex VI list): Carc. 1B H350 | Prop 65 cancer, 1988-01-01 |
| formaldehyde released from MBO (66204-44-2) and HPT | biocides (formaldehyde releasers) | 612-290-00-1 (MBO) and 612-291-00-7 (HPT): Carc. 1B H350, Muta. 2 H341, STOT RE 2 H373, Skin Sens. 1A H317 and further acute, corrosive and aquatic classes (ATP10, Reg. (EU) 2017/776, since 2018-12-01) | formaldehyde (gas): IARC Group 1; Prop 65 cancer, 1988-01-01 |
| HHT triazine (4719-04-4) | biocide (formaldehyde releaser) | 613-114-00-6 (original Annex VI list): Acute Tox. 4 H302, Skin Sens. 1 H317 | no carcinogenicity class |
| MIT (2682-20-4) and C(M)IT/MIT 3:1 (55965-84-9) | biocides | 613-326-00-9 and 613-167-00-5 (ATP13): H301, H311 (MIT) or H310 (C(M)IT/MIT), H314, H317, H318, H330, H400, H410; Skin Sens. 1A with SCL 0.0015 % (15 ppm) | C(M)IT/MIT PT13 label condition (Impl. Reg. (EU) 2016/131) |
| IPBC (55406-53-6) | fungicide | 616-212-00-7 (ATP06, Reg. (EU) 605/2014, since 2015-04-01): Acute Tox. 3 H331, Acute Tox. 4 H302, STOT RE 1 H372, Eye Dam. 1 H318, Skin Sens. 1 H317, H400, H410; Acute Tox. 2 H330 replaces H331 from 2027-02-01 (ATP23, Reg. (EU) 2025/1222) | 4.6 % positive (IVDK 2010 to 2018) |
| 2-mercaptobenzothiazole, MBT (149-30-4) | yellow-metal inhibitor | 613-108-00-3 (original Annex VI list): Skin Sens. 1 H317, H400, H410 | IARC Group 2A (Vol. 115); Prop 65 cancer, 2017-10-27 |
| rosin, colophony (8050-09-7) | emulsifier component, rarely declared | 650-015-00-7 (original Annex VI list): Skin Sens. 1 H317 | 11.4 % positive (IVDK 2010 to 2018) |
CLP lines from ECHA CHEM Annex VI as of 27 October 2026; a product's own classification is on its safety data sheet.
Nine of the eleven rows are metalworking fluid additives, and every class of metalworking fluid additives, with its treat rate and regulatory flag, is described on the additives hub.
Nitrosamines from amines and nitrite#
N-nitrosodiethanolamine (NDELA), classified Carc. 1B H350 under CLP Annex VI (index 612-090-00-4, original Annex VI list), forms in water-mix fluids when a secondary amine meets a nitrosating agent. Diethanolamine is such an amine, and sodium nitrite such an agent. A UK survey of in-use water-mix fluids found a median NDELA level of 0.4 µg/mL (0.4 mg/L) in the diluted fluid (PubMed 12505903).
Formaldehyde-releasing biocides in the sump#
Formaldehyde released from the biocides MBO (index 612-290-00-1) and HPT (612-291-00-7) is classified Carc. 1B H350 and Muta. 2 H341 under ATP10 (Regulation (EU) 2017/776) since 1 December 2018. HHT triazine (613-114-00-6, original Annex VI list), by contrast, carries only Acute Tox. 4 H302 and Skin Sens. 1 H317. One Finnish study measured total formaldehyde of 0.002 to 1.3 % of the concentrate in all 17 concentrates tested, none of which declared it on the safety data sheet (PubMed 18976375).
Skin sensitizers in the concentrate#
Monoethanolamine is the most frequent metalworking fluid allergen, positive in 12.6 % of 804 patch-tested cutting metalworkers (IVDK, 2010 to 2018), ahead of colophonium at 11.4 %. Formaldehyde releasers follow at up to 8.5 %, and formaldehyde and IPBC at 4.6 % each, in the same patch-test series (PubMed 32776554). Monoethanolamine carries no CLP sensitizer class, while MIT and C(M)IT/MIT are Skin Sens. 1A with a specific concentration limit of 0.0015 % (15 ppm).
How Is Exposure to Metalworking Fluids Controlled?#
Metalworking fluid safety rests on a managed system of engineering controls, fluid management, work practices and personal protective equipment. The OSHA Metalworking Fluids Best Practices Manual sets this system out as voluntary guidance that creates no legal obligation. Its fluid management program monitors concentration, pH, microbial levels, tramp oil and suspended solids, and cleans the system before each recharge.
Substitution comes first. The OSHA manual advises avoiding oils that contain polycyclic aromatic hydrocarbons, chlorinated paraffins, alkanolamines, nitrites and formaldehyde-releasing biocides. Metalworking fluids in specification also hold exposure down, and the routines that keep metalworking fluids in specification control concentration, tramp oil and microbes.
Engineering controls follow: machine enclosures are the most effective control for mist (OECD ESD No. 28, 2011), and local exhaust ventilation comes next. Respirators belong only where these controls and work practices do not hold exposure down, under the OSHA respiratory protection standard 29 CFR 1910.134.
Safety precautions when using cutting fluids#
The eight precautions below follow HSE and OSHA guidance.
- Check fluid concentration, pH, bacteria and sump temperature weekly, and keep tramp oil below 2 % by volume (HSE MW5, 03/21).
- Keep machine doors closed until no mist reaches the breathing zone, 20 to 30 cm (8 to 12 in) from nose and mouth (HSE MW1).
- Set compressed-air blow-off as low as practicable, as a guide 2.1 bar (30 psi) (HSE MW1).
- Have local exhaust ventilation thoroughly examined at least every 14 months, and keep the records for at least 5 years (HSE MW1).
- Wear single-use nitrile gloves where there is no entanglement risk, and thicker gloves for cleaning and maintenance (HSE MW2).
- Treat barrier creams as a supplement to gloves, never a replacement (OSHA).
- Use respirators only where engineering controls and work practices do not control exposure (OSHA, 29 CFR 1910.134).
- Report skin or breathing symptoms early to health surveillance (NIOSH, OSHA manual).
Air monitoring and medical surveillance#
Air monitoring for metalworking fluid aerosol runs at least once a year, every 6 months where results reach half the NIOSH REL, and after any significant process change (NIOSH, as published in the OSHA manual). The four elements of the NIOSH medical surveillance program are listed below.
- Lung examination
- Respiratory questionnaire
- Baseline spirometry to American Thoracic Society criteria, by NIOSH-trained staff
- Skin examination
Metalworking fluid air sampling by NIOSH Method 5524 (Issue 2, 29 December 2014) collects the thoracic or total fraction on a tared 37 mm, 2 µm PTFE filter, and the metalworking fluid air sampling page explains how results compare with the NIOSH REL.
Is there a legal exposure limit for metalworking fluids?#
No US federal limit exists for metalworking fluids as such: OSHA has no metalworking-fluid standard or PEL. The NIOSH recommended exposure limit of 0.4 mg/m³ thoracic particulate mass (about 0.5 mg/m³ total particulate mass), as a time-weighted average for up to 10 hours a day in a 40-hour week (Criteria Document 98-102, January 1998), is a recommendation, not an enforceable limit. In Great Britain, the HSE sets no workplace exposure limit for metalworking fluids or mineral oil mist (EH40/2005, fourth edition, 2020).
What Else Affects Metalworking Fluid Safety?#
Beyond the fluid formulation, the microbes that grow in the sump, the metals dissolved from the workpiece and the duties placed on employers shape how hazardous a metalworking fluid becomes in use. Endotoxin from sump bacteria, nickel from the workpiece and the COSHH duty are one example of each.
Sump bacteria and endotoxin#
Coolant bacteria in the sump release endotoxin, which causes airway irritation and fever 5 to 6 hours after exposure that subsides in about 24 hours (DGUV). A UK sump survey found medians of 109,000 CFU/mL bacteria and 8,039 EU/mL endotoxin in the fluid (PubMed 12505903). Dip slide checks of coolant bacteria track fluid condition, not health risk.
Metals from the workpiece in the fluid#
Workpiece metals add skin allergens to the fluid: 13 of 80 Danish metalworking fluid samples held more than 1 mg/kg nickel (PubMed 32212165). Nickel levels were similar in used and unused fluid, and one sample in the same study held 1.3 mg/kg cobalt, the metal that carbide grinding adds to the fluid.
What the rules require of employers#
Employers in Great Britain must prevent or adequately control exposure to metalworking fluids under the COSHH Regulations 2002. In the EU, the PT13 approval of C(M)IT/MIT (Implementing Regulation (EU) 2016/131) requires labels saying not to use it in metalworking fluids at a concentration that classifies the fluid as a skin sensitizer.
In the US, metalworking fluid regulations rest on general standards: the OSHA manual is advisory, and only the general PELs for mineral oil mist and for particulates not otherwise regulated apply. The metalworking fluid regulations hub lists each instrument with its article and date.
FAQ#
Is machine shop coolant hazardous?#
Yes: machine shop coolant causes dermatitis and respiratory disease when skin contact and mist are not controlled, whatever its type (HSE). Machining coolant without a CLP classification can still cause dermatitis, asthma or hypersensitivity pneumonitis.
Do barrier creams replace gloves?#
No: barrier creams showed no significant effect on cutting-fluid dermatitis over 6 months in new machinists in one study (PubMed 7821012). OSHA treats them as a supplement only, and HSE guidance MW2 accepts single-use nitrile gloves where there is no entanglement risk.
Who should a worker with skin or breathing symptoms see?#
An occupational physician assesses skin or breathing symptoms linked to metalworking fluids. Health surveillance under COSHH and the NIOSH-recommended spirometry and skin examinations exist to find such symptoms early.