What Persistent Chemical Odors in Your Histology Lab Really Mean

Many labs live with a persistent chemical odor that staff eventually stop noticing. Histotechs often become desensitized after years of working around formalin, xylene, and alcohol vapors. Even though the odor does not seem strong to those in the lab, it can still affect your health and comfort, and it can impact everyone else in the building who walks by your door. A smelly histology lab is not just a nuisance, it is a warning sign of elevated volatile organic compounds and inadequate fume control.

This blog explains why these odors occur, the effects of common histology vapors, the recommended exposure limits, and what you can do to eliminate the smell and create a safer lab environment.

Why Histology Labs Often Smell Bad

Histology labs use large volumes of three major chemicals that generate airborne vapors.

Formaldehyde (formalin)

This is a known irritant and carcinogen. Even very low concentrations create a sharp, noticeable odor. Short-term exposure causes headaches, eye and throat irritation, and respiratory discomfort. Long-term exposure can lead to chronic coughing, wheezing, worsening asthma, recurring sinus irritation, and neurological symptoms such as headaches, fatigue, dizziness, and difficulty concentrating. Extended exposure increases the risk of respiratory disease and certain cancers, including nasopharyngeal cancer and leukemia.

Xylene

A strong aromatic solvent used in processing and staining. It readily evaporates into the air. Chronic exposure can cause fatigue, dizziness, and central nervous system effects, and even small leaks in equipment or containers can create noticeable odors.

Alcohols

Less hazardous than formalin and xylene but still irritating when concentrated. Spills, open
containers, and frequent reagent changes all release alcohol vapors that accumulate if ventilation is inadequate. 

With repeated occupational exposure, olfactory receptors undergo adaptive desensitization, resulting in a diminished perception of formaldehyde, xylene, and alcohol vapors over time.

Personnel who work in the laboratory each day therefore experience reduced odor awareness, while individuals without chronic exposure, including visitors, administrators, pathologists, and other non-laboratory staff, detect the fumes immediately due to the absence of olfactory adaptation. Many labs exceed the action level without realizing it. If detectable odors are present in the laboratory, it strongly suggests that volatile chemical concentrations are elevated above acceptable levels and may be approaching or exceeding thresholds that warrant corrective action and controls.

Understanding Allowed Levels for Formaldehyde and Xylene

Formalin and xylene are the two most heavily regulated chemicals in histology due to their respiratory, neurological, and long-term health effects. The Occupational Safety and Health Administration establishes strict exposure limits for both substances to protect laboratory personnel from acute and chronic toxicity.

Formaldehyde Exposure Limits (OSHA 29 CFR 1910.1048)

Because formaldehyde is a known carcinogen and potent irritant, OSHA mandates the following limits:

• Permissible Exposure Limit, 0.75 parts per million as an eight-hour time-weighted average
• Short Term Exposure Limit, 2.0 parts per million during any fifteen-minute period
• Action Level, 0.5 parts per million as an eight-hour TWA

These thresholds trigger requirements for exposure monitoring, engineering controls, medical surveillance, and hazard communication.

Xylene Exposure Limits (OSHA 29 CFR 1910.1000 Table Z-1)

Xylene is a central nervous system depressant and mucous membrane irritant that readily accumulates in processing and staining areas.

• Permissible Exposure Limit, 100 parts per million as an eight-hour time weighted-average
• Short-Term Exposure Limit, 150 parts per million during a fifteen-minute exposure

Common Sources of Excess VOCs in Histology Labs

• Leaking reagent containers
• Open or uncovered reagent containers, processing and staining vessels
• Emptying and refilling reagent containers without a fume containment hood
• Saturated carbon filters in equipment
• Inadequate ventilation or blocked airflow

Even one of the above issues can cause the entire lab to smell.

Best Practices for Handling and Refilling Reagents

Reducing odors requires consistent and disciplined chemical handling.

• Always work under a certified fume hood when pouring, filling, or disposing of reagents
• Keep formalin and xylene containers tightly sealed when not in use
• Handle reagents slowly to reduce splashing and vapor release
• Do not leave open containers on countertops or inside equipment
• Dispose of waste promptly and keep waste vessels sealed
• Clean up chemical residues and spills immediately

Ideal Solution to Remove Chemical Vapors

The true ideal solution for long-term odor control is a complete laboratory-grade ventilation system that removes chemical vapors through a dedicated building-level exhaust. These engineered exhaust systems capture fumes at the source and evacuate them outdoors where they cannot accumulate in the lab or migrate to other areas of the facility.

This approach is extremely effective, but it also comes with practical challenges. A building-level ventilation system is expensive to install, requires engineering approval, and often demands major remodeling. Many labs would need to shut down or significantly reduce operations while the ventilation project is completed. For hospitals and clinics that cannot afford extended downtime, or for private practices with limited renovation budgets, this ideal solution is not always realistic.

Because of these constraints, most labs rely on a combination of equipment filtration, fume hoods, and high-capacity carbon-based filtration units to control VOCs.

Why Activated Carbon Works and Why It Must Be Replaced

Activated carbon is used in many histology instruments to control fumes in enclosed systems such as tissue processors, stainers, and coverslippers. Carbon does not absorb chemicals the way a sponge absorbs water. Instead, it adsorbs molecules. Vapors adhere to the enormous internal surface area of the carbon granules.

However, once the carbon becomes saturated, it can no longer capture vapors. At that point, fumes simply pass through the filter and escape into the lab. This is why routine replacement of carbon filters is essential for maintaining safe VOC levels.

You can find activated carbon filters for Leica, Sakura, Thermo, and other instruments here:
Rankin Biomedical Carbon Filters

If odors persist after replacing these filters, your lab may be producing more fumes than the machines are capable of managing on their own.

When Equipment Filters Are Not Enough

Many labs assume that the internal carbon filters in their tissue processors or stainers will control all fumes. In reality, these filters were designed to reduce local emissions inside the machine, not to clean the entire room. Large volumes of formalin, xylene, and alcohol vapors require true room-level air purification.

If your lab continues to smell despite good chemical handling and new machine filters, you likely need supplemental air scrubbing.

Eliminating Odors with Recirculating Filter Systems

For labs struggling with persistent VOC levels, the most reliable solution is to add one or several high-capacity carbon filtration systems. Rankin’s CAN filter systems provide powerful air scrubbing that continuously circulates air, removes VOCs, and restores a clean and odor-free environment.

Because every lab has a unique size and air volume, some facilities need one unit, while others require multiple units positioned strategically throughout the lab.

You can explore the available CAN filter systems here:
Rankin Biomedical CAN Filter Systems

These units supplement your existing equipment filters and provide extremely powerful VOC removal necessary to keep air quality compliant and comfortable.

A persistent chemical odor in a histology laboratory should never be ignored. Persistent chemical odors are a symptom of elevated VOCs, inadequate filtration, or inconsistent reagent handling. Even if you no longer notice the smell, it affects your coworkers and can pose a real health risk.

By replacing internal carbon filters on schedule, improving reagent handling practices, considering a dedicated ventilation system when feasible, and using supplemental CAN filter systems when necessary, you can keep your lab compliant, improve air quality, and create a safer and more pleasant workplace for everyone.