A Review of Occupational Safety of Phenol Use in Podiatric Practice

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By Bethany Robinson, BS

Podiatrists commonly use phenol, also known as carbolic acid, in chemical matrixectomy procedures when treating ingrown toenails. First documented for that use by Boll in 1945,¹ phenol is a volatile organic compound, that poses a risk for both local and systemic toxicity. While numerous studies have evaluated the safety of phenol for patients, fewer have explored its occupational safety for healthcare professionals, especially podiatrists.

Phenol was widely used in the nineteenth century as a surgical antiseptic in soaks, sprays, and ointments. Many health care workers exposed to phenol at that time reported symptoms such as anorexia, nausea, headache, and dark urine, a constellation of signs referred to as “phenol marasmus.”² Today, similar symptoms, including nausea, headaches, and transient vertigo, are still reported by podiatrists during or after phenol-based procedures.

What Does the Literature Reveal About Phenol Exposure?

Deichmann and colleagues investigated the effects of prolonged phenol inhalation in animals. Researchers exposed rabbits, rats, and guinea pigs to phenol vapors at concentrations of 0.1 to 0.2 mg per liter for 7 hours a day, 5 days a week. Guinea pigs exhibited signs of distress and illness, including respiratory difficulty, weight loss, and paralysis after 20 exposure sessions. Postmortem examinations revealed acute toxicity in the lungs, heart, liver, and kidneys.³ Rabbits showed no outward signs of illness after 63 exposure periods but had progressive pulmonary inflammation and injury upon examination.³ Rats displayed no signs of illness or postmortem organ damage after 53 exposure periods.³ 

To evaluate human occupational exposure in clinical settings, Iglesias and team measured phenol vapor inhalation for physicians and assistants during chemical matrixectomy of bilateral nail borders.⁴ They measured environmental concentrations of phenol vapor in the breathing zones of the physician and assistant in a closed treatment room lacking natural ventilation or a gas extraction system. The procedure utilized a 95% phenol solution in a 50 mL bottle, remaining open during 6, 1-minute applications for a total of 6 minutes. Sampling lasted 21 minutes, during which the phenol concentration measured for the zones of respiration of the physician and the assistant were 1.2 and 0.2 parts per million (ppm).⁴ Both values are below phenol’s environmental limit of daily exposure set by Spain’s National Institute of Safety and Hygiene in the Workplace in 2007 of 2 ppm.⁵ The concentration measured in the physician’s respiration zone had an index of exposure of 60% of Spain’s environmental limit of daily exposure (1.2/2.0 x 100).^4,5 

Vallejo and coworkers examined urinary phenol excretion in physicians after unilateral nail matrix phenolization.⁶ Twenty-five physicians participated, with exclusion criteria including chronic disease or pregnancy. A 90% phenol solution in a 50 mL bottle remained open for 6 minutes while the physician performed 3, 1-minute applications. The procedure occurred in closed patient rooms lacking natural ventilation or gas extraction systems, and physicians wore face masks during the procedures, although the researchers did not specify the type of mask used. The duration of sampling was measured from the time they opened the bottle of phenol until completion of the procedure and departure of the medical personnel from treatment room, with average exposure times ranging from 14 to 21 minutes. Collection of the urine samples took place 2, 4, 6, 8, 10, 24, 48, and 72 hours after the procedure. The highest concentration of urinary phenol was within the first 2 hours after exposure, at almost 10 mg/L.6 Concentrations declined approximately 1 mg/L every 2 hours for the first 10 hours and reached 3 mg/L by 72 hours post-exposure.⁶ All values remained within normal limits and below the occupational safety limit of 20 mg/L set by Spain’s National Institute for Safety and Hygiene in the Workplace.⁵ 

Considering Podiatric Applications

In August 2021, NHS England, the British Orthopaedic Association, and the Royal College of Podiatry issued a joint alert advising the elimination of multi-use 80% phenol bottles.⁷ This followed incidents involving phenol being mistaken for other medications and causing burns when spilled. The alert recommends replacing multi-use bottles with safer alternatives. Single-use phenol packets may reduce respiratory exposure and the risk of spillage or skin contact by limiting the volume of exposed phenol.⁷

The Occupational Safety and Health Administration (OSHA) has established a permissible exposure limit (PEL) for phenol of 5 parts per million (ppm) as an 8-hour time-weighted average (TWA).⁸ According to The National Institute for Occupational Safety and Health (NIOSH) guidelines, respiratory protection is not required for podiatrists when exposure levels remain below this threshold.⁹ The previously mentioned study that measured phenol exposure during bilateral matrixectomies and found an average concentration of 1.2 ppm over a 21-minute sampling period, well below the OSHA limit.⁴ Nonetheless, minimizing exposure to all hazardous substances remains a priority. Strategies such as using single-use phenol packets, ensuring adequate ventilation, and implementing proper disposal procedures for phenol-contaminated materials can significantly reduce occupational risk.

The safety of phenol use by pregnant healthcare workers remains unclear. Animal studies have shown reduced fetal weight, growth retardation, and developmental abnormalities following oral phenol exposure, but limited human data exists.¹⁰ OSHA’s phenol exposure limits do not (explicitly) account for (address potential) reproductive or developmental toxicity. Pregnant women should follow standard recommendations – but with added caution. The safest approach is to minimize all unnecessary exposure.

In Conclusion

Phenol is a long-standing tool utilized by podiatrists, and by and large, the literature supports its occupational safety when used under the proper protocols and circumstances, while limiting unnecessary exposure. Further research could be illuminating examining the relative exposure of single-use phenol packets, the influence of room ventilation, and the impact for pregnant healthcare professionals. 

The author is a fourth-year podiatric medical student at Midwestern University Arizona College of Podiatric Medicine.

Lead photograph courtesy of Tracey Vlahovic, DPM