While the histopathology laboratory has progressively become more efficient, with a vast diversity in applications and techniques, the replication and monotony of routine tasks have caused some of the most basic safety and security practices to become overlooked or even forgotten. We focus on strict adherence to protocols; we highlight critical steps in procedure; we arduously labor to manage an increase in work volume. But the simplest, elementary, ‘no brainers’ of personal safety, such as our hands, our eyes, our skin, and lungs; these things are regularly disregarded in the daily completion of workflow. This 2-part series will discuss aspects of safety; first in personal safety applications we physically and independently practice, and second, in equipment and devices that are designed to enhance the safety of the workplace in general.

How often do we see technologists begin the brief handling of reagents, stains and/or chemicals without first putting on gloves? Granted, the putting on/taking off of gloves can be more time/trouble than the act of dumping or re-filling a reagent. After doing something like this, how often do we see the technologist carry on with other duties in the lab without washing hands. These are two examples of routine operation done as unconsciously as turning on the lights or power of an instrument. Little thought is given to skin irritants and the inflammatory response that can come from a small splash drop of a chemical such as xylene. Our brain does not send off the same warning sign as it does when working with acids.

Xylene is a perfect example of a chemical we have become so comfortable with because many histologists have developed a tolerance to low level exposures, such to the point that even when the exposure amount is moderately increased, we still experience no major intolerable effects. Xylene is a benzene derivative (dimethyl benzene) with regulated exposure limits due to its toxicity and effects on the nervous system. It is by far the most widely used and effective solvent employed in routine histology. Its efficiency as a solvent is due to its strong ability to displace alcohol and enhance the tissue’s ability to be infiltrated by paraffin wax. It is the perfect clearing agent for tissue processing, and for deparaffinization of slides (dewaxing) before staining.

Unfortunately, xylene can have detrimental effects with short and long-term exposures. Xylene breaks down the skin’s natural protective oils and easily penetrates into the skin. With minute drops or splashes that are allowed to dry or absorb into the skin, irritation can occur leading to dermatitis. Dryness, flaking, and cracking of skin may occur, and previously exposed or damaged skin, because the natural oils have been removed, make the skin more easily accessible to even greater absorption. With the air environment, there are permissible exposure limits. The Occupational Safety and Health Administration (OSHA) sets a permissible exposure limit for 100 ppm per 8-hour time-weighted average. The National Institute for Occupational Safety and Health (NIOSH) recommends an exposure limit at 100 ppm per 10-hour time weighted average, a 40-hour/week cumulative average, and a short-term limit of (10-minutes) for environments of 200 ppm.


Effect of Xylene on the Nervous System

100–200 ppm Nausea, headache
200–500 ppm Feeling “high,” dizziness, weakness, irritability, vomiting, slowed reaction time
800–10,000 ppm Giddiness, confusion, clumsiness, slurred speech, loss of balance, ringing in the ears
>10,000 ppm Sleepiness, loss of consciousness, death


The table above shows the detrimental effects of permissible and greater than ppm exposures to xylene. It is noted that the type and severity of health effects can depend on several factors, including the amount of xylene vapor you are exposed to and the length of time you are exposed in that environment. Individuals also react differently to various levels of exposure, making the reaction occurrence variable and difficult to predict between persons.

Xylene is just the example used in this article to emphasize the point that common elementary safety practices must be mandated in histopathology practices. Exposure to this in the histology lab, as well as other chemicals, occurs most commonly through inhalation, skin or eye contact, or even clothing. Many histology laboratories have a very loose policy on the wearing of personal protective equipment (PPE) clothing such as lab coats and/or aprons. It should be noted that xylene becomes easily trapped in regular clothing, and the dried nature of this chemical can/will continue to be an irritant to the skin and cause blistering and chemical burns. The seeming inconvenience of wearing a lab coat is insignificant to the potential of carrying unseen chemical residue on your clothing back to your home to be exposed to family, pets, etc.

Even the most elementary and common forms of safety; from safety glasses, to masks, to lab coats, and even the ‘no brainer’ practice of hand washing; all of these play an important and significant part of protecting yourself. These items have been created based on a history of avoidable accidents that caused bodily injury, from small skin irritations, to serious eye damage. Let us not increase our risk towards accidents simply because we did not take the small precautions serious enough to eliminate the potential. An accident is and will eventually happen if we do not practice safety.


  • Brown,S., “Enhancing PPE Methods During Covid-19 Crisis”, Labstore Highlights, 2020.

  • Kandylala, R., Raghavendra,S., Rajasekharan, S., “Xylene: An Overview of Health Hazards”, JOMFP, Jan. 2010.

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