As the nation’s 375,000 nail technicians buff, polish and file our fingers and toes, that workplace exposure to chemicals in the polish and glue can pose a real threat. But it’s not just the amount of those substance that can turn them toxic, it is also the way they get into workers’ bodies.

Workplace conditions in certain nail salons, expertly laid out last week in an investigation by The New York Times’s Sarah Maslin Nir, can alleviate or exacerbate these issues. Chemicals inside of the glues, removers, polishes and salon products—which technicians are often exposed to at close proximity and in poorly ventilated spaces—can be hazardous individually. When combined, however, they could potentially cause even greater harm. Yet it is difficult to know how these chemicals affect the body because current evaluations do not look at these substances comprehensively. There are also few reports looking at how each compound individually affects nail workers.

The risks are many: Dust shavings from filed nails can settle on the skin like pollen and cause irritation or can be inhaled (and those small particles could contain chemicals from the polishes or acrylics). Technicians could also inhale harmful vapors or mists from the chemicals in the shop. The compounds could also settle into workers’ eyes. Moreover, these substances could be swallowed while eating, drinking or puffing on a cigarette during a break.

The U.S. Occupational Safety and Health Administration (OSHA), which sets workplace safety standards, cites a laundry list of chemicals that nail salon workers encounter daily. For the typical nail salon client these chemicals may not pose a large threat, but for workers who are exposed to this potentially toxic brew day after day there’s an elevated level of risk. Studies documenting the health problems of nail technicians often describe respiratory, skin and musculoskeletal issues. Respiratory problems, unsurprisingly, were typically associated with the reporting of workplace exposures such as poor air quality. Some of these chemicals are also linked with birth defects. Yet, as with many environmental exposures, it can be difficult to prove that an adverse health effect was the direct result of workplace exposures instead of those encountered elsewhere in life.

Nail salons could help protect workers by providing certain safety equipment. Public health officials say wearing nitrile gloves (not latex or vinyl) could help shield workers from chemical exposures. Using a proper mask to protect workers from chemicals or nail-filing dust would also help. Paper dust masks (like those most often seen in a salon), however, only protect the wearer from some dusts but not chemicals. Good ventilation in a nail salon would also typically eliminate the need for workers to wear heavy-duty respirator masks with organic vapor cartridges.

Here’s the latest science on four nail salon chemicals of particular concern:

Toluene

This clear, colorless liquid occurs naturally in crude oil. It’s also a common ingredient in nail polish and fingernail glue. Inhaling high levels of this substance in a short period can produce light-headedness, dizziness or drowsiness. Yet significant exposures can also damage the nervous system as well as irritate eyes, throat and lungs. Studies indicate that breathing high levels of the substance during pregnancy can cause birth defects, slow growth and retard mental abilities of the offspring. So how much toluene is too much? OSHA has set a limit of 200 parts toluene per million during an eight-hour work shift. California, however, has set its own limit at 10 parts toluene per million for the same period. Yet the only way to know if one’s workplace surpasses these limits is with air monitoring. Humans can smell toluene even below the OSHA threshold—and even if someone cannot detect this chemical, that could be simply because one’s sniffer grew used to it.

Formaldehyde

This substance is used in nail polish and nail hardener. Studies indicate it can cause cancer. It can also irritate the eyes, skin and throat, inducing coughing, allergic reactions, asthma-like attacks or difficulty breathing. Workers are advised by OSHA that wearing half-mask respirators with chemical cartridges can protect them from inhaling these vapors. Because even at low concentrations (like 0.1 to 0.5 part per million) this substance can irritate the nose and eyes and has been shown to decrease performance on short-term memory tests.

Dibutyl Phthalate

This substance is often used to make plastics softer and more flexible, and small amounts are used in nail polish and polish hardener. Little definitive information exists on how the chemical affects humans long-term in the U.S. OSHA warns that exposure in humans can cause nausea and irritation to the respiratory tract and eyes. The effects are much more concerning in animals—when rodents were orally exposed to this man-made chemical, it was shown to cause developmental and reproductive issues: Problems included birth defects in mice, decreased number of viable litters and reduced fetal birth weight. The state of California classifies it as a reproductive and developmental toxicant in humans.

Methacrylate Compounds

Ethyl methacrylate (EMA) is the main substance in artificial fingernails. The substance can be problematic for both nail technicians and customers, causing allergies, asthma and dermatitis. To get around that risk, artificial fingernails should be applied at a ventilated worktable, according to the National Institute for Occupational Safety and Health. NIOSH advises workers removing artificial nails to wear safety glasses to protect their eyes as well as long sleeves and gloves to protect their skin from acrylic dust.

Avoiding these substances altogether remains challenging. Some nail products are labeled as “3-free”—which, if their labels are accurate, would mean they were free of toluene, formaldehyde and dibutyl phthalate. Analysis of some such products by the California Department of Toxic Substances Control, however, finds those labels are often inaccurate. Primers labeled as “acid free” are also typically claiming to be free of chemicals like methacrylate acid.

Unfortunately, workers have to worry about more than chemical risks. Nail technicians can develop aches and pains from bending over or being in the same hunched position for long periods. They are also at risk of acquiring an infection from contact with client’s nails, blood or skin as they are filing and buffing. Here, too, protective masks and gloves can help keep workers safe. So next time you go for a manicure or pedicure, look around and see if workers are bedecked in gloves and masks, and if the tables seem to be ventilated. Everything may not be apparent to the eye but it will at least give you some initial indications. And if workers are unprotected, perhaps choose another salon.