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Phenol Matrixectomy in Pregnancy and Breastfeeding: Correction of Exposure Calculations and Implications for Clinical Risk Assessment

Submitted:

25 September 2026

Posted:

29 September 2026

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Abstract
Background: Phenol matrixectomy is widely utilised to manage onychocryptosis. Concerns regarding its safety in pregnancy and breastfeeding persist, despite limited direct evidence of adverse events. Previous work by the authors suggested that systemic phenol dosage to a pregnant woman during nail surgery was negligible; however, a subsequent review of that publication identified a mathematical calculation error and an underestimation of phenol dose.Methods: We conducted a narrative critical review in 2022, drawing on clinical, toxicological, occupational, and epidemiological literature, including original work. We recalculated exposure estimates and contextualised them against established toxicological thresholds.Results: Epidemiological studies demonstrate widespread background exposure to a range of phenolic compounds during pregnancy, with inconsistent associations with adverse outcomes. Animal studies indicate developmental toxicity at high systemic doses. Corrected calculations demonstrate that phenol exposure during nail surgery may be substantially higher than we previously reported; however, actual systemic phenol absorption remains unknown. Conclusion: Phenol exposure during matrixectomy remains a risk-uncertain intervention because the lack of pharmacokinetic data prevents definitive risk assessment.
Keywords: 
nail surgery
;  
pregnancy
;  
breastfeeding
;  
phenol
;  
toxicology
;  
matrixectomy
;  
exposure modelling
Subject: 
Medicine and Pharmacology  -   Pharmacology and Toxicology

Introduction

Phenol (monohydroxybenzene) (C₆H₅OH) is the parent of the class of chemicals containing one or more hydroxyl groups attached to an aromatic ring (Weber, Weber and Weber, 2020), see Figure 1. Also known as carbolic acid, it is the simplest phenolic compound; many of its derivatives are natural substances widely distributed throughout the environment (Agency for Toxic Substances and Disease Registry (ATSDR), 2008). Phenol is systemically bioavailable, absorbed via dermal, inhalational, and oral routes, and is associated with both local and systemic toxicity (Bruce, Santodonato and Neal, 1987).
Chemical matrixectomy with phenol causes protein denaturation and coagulative necrosis of the nail matrix and is an established and effective intervention for ingrown toenails, with widespread evidence supporting its role in reducing recurrence rates (Bostanci, Gürgey and Ekmekci, 2001; Boberg, Frederiksen and Harton, 2002; Eekhof et al., 2012; Exley et al., 2023b, 2023a). Although the available evidence suggests that phenol exposure at non-toxic levels is unlikely to adversely affect foetal development (UK Health Security Agency, 2024), uncertainty persists about phenol’s safety during pregnancy and breastfeeding despite its use for many decades (Iglesias et al., 2008; Becerro De Bengoa Vallejo et al., 2012; Robinson, 2025). This creates a clinical paradox: phenol is both commonly encountered and poorly researched for procedural use during pregnancy. Previous work by the authors (Reilly, Ousey and Blandford, 2022) concluded that exposure during nail surgery was negligible; however, a re-evaluation has identified a fundamental error in the exposure estimate.
This study aims to critically re-evaluate phenol exposure in nail surgery by correcting prior modelling errors and contextualising the revised exposure within available toxicological and clinical evidence. This paper adopts a critical narrative review approach, focusing on:
  • Toxicological data on phenol exposure
  • Occupational and environmental exposure literature
  • Previously published exposure calculations in podiatric contexts
  • Recalculation of phenol dose using corrected physical parameters

Methods

We conducted searches between January 2022 and March 2026. Sources were selected for relevance to phenol toxicology, pregnancy exposure, occupational exposure, and clinical use in matrixectomy. Literature sources included:
  • Electronic databases (MEDLINE, EMBASE, CINAHL, AMED)
  • Reference lists from key studies
  • Toxicological and regulatory reports
Search terms included combinations of:
phenol, pregnancy, breastfeeding, toxicology, exposure
Given the heterogeneity of available evidence, a structured narrative synthesis approach rather than a formal meta-analysis. Exposure modelling was re-derived using:
  • manufacturer data for phenol swab volume
  • density-based conversion to mass
  • scenario-based absorption estimates
Phenol exposure in context 
Environmental and background exposure 
Phenols are consistently detected in human biological samples. Large cohort studies (Walkley, Pagnotto and Elkins, 1961; Wolff et al., 2008; Philippat et al., 2012, 2014; Chen et al., 2013; Tang et al., 2013; Guidry et al., 2015; Vélez, Arbuckle and Fraser, 2015; Ashrap et al., 2018; Ferguson et al., 2018; Aker et al., 2019; Barkoski et al., 2019; Nakiwala et al., 2020; Rolland et al., 2020; Zhang et al., 2021; Jedynak et al., 2022) demonstrate high detection rates (>90%) in pregnant populations with repeated exposure throughout gestation. Much of this literature concerns a broad range of phenolic compounds rather than monohydroxybenzene specifically, limiting direct applicability to procedural phenol exposure. Some phenols, notably pentachlorophenol and benzophenone-3, have been associated with foetal growth parameters and endocrine disruption. However, findings are inconsistent and reflect chronic low-dose exposure, limiting comparability with procedural exposure.
Occupational and clinical exposure 
Clinical exposure in dermatology (e.g. phenol peels) demonstrates that phenol can be systemically absorbed through skin, with toxicity observed at higher doses (Landau, 2008). Occupational exposure studies demonstrate that phenol vapour is detectable during matrixectomy but generally remains below workplace exposure limits (Iglesias et al., 2008). However, that study primarily assesses airborne concentration rather than dermal absorption.
Toxicological evidence 
Animal studies outlined in our earlier paper (Reilly, Ousey and Blandford, 2022) demonstrated dose-dependent developmental toxicity, including reduced foetal weight and structural abnormalities at high exposure levels. These effects are typically observed in the presence of maternal toxicity and at doses substantially exceeding environmental exposure levels. Human data remain limited and inconclusive. Studies of occupational exposure to organic solvents, including phenols, suggest possible associations with adverse pregnancy outcomes, although causality is unclear (Rosen Vollmar et al., 2023).
Correction of exposure calculations 
In the UK, phenol swabs, originally marketed as EZ swabs but now as Swab-it, contain 0.15 mL and 0.20 mL of 89% phenol USP (DLT Podiatry Supplies, no date), see Figure 2. It is a Class IIa licensed medical device manufactured in accordance with ISO 13485.
The authors’ original work assumed that each phenol swab contained 0.178 mL of 89% phenol, yielding 0.178 mg per swab (if 100% of the phenol is transferred). The mistake was a unit-conversion error between mL and mg, compounded by failure to account properly for the concentration expression and density. The corrected calculation is:
Density:
  • 1.05 g/mL = 1050 mg/mL (Valeant Pharmaceuticals North America, 2015)
Phenol concentration:
  • 89% × 1050 mg/mL = 934.5 mg/mL 
Doses:
  • 0.15 mL × 934.5 mg/mL = 140.175 mg 
  • 0.20 mL × 934.5 mg/mL = 186.9 mg 
The phenol is typically delivered using two to three swabs or applicators for three minutes before irrigation and lavage of the nail sulcus (Exley et al., 2024). Therefore, the dose for three swabs is:
  • 0.15 mL (140.2 mg) × 3 = 420.5 mg 
  • 0.20 mL (186.9 mg) × 3 = 560.7 mg 
This is approximately 800–1,050-fold higher than previously reported (≈ three orders of magnitude.
Applied vs systemic dose 
Applied phenol does not equate to systemic exposure. During matrixectomy:
  • Some phenol remains on the swab
  • Some phenol evaporates
  • Some phenol is partially neutralised by tissue proteins
  • Some phenol is removed during irrigation
While phenol is known to be readily absorbed through the skin and mucosa, no published data currently quantify the fraction absorbed into the systemic circulation or plasma phenol levels post-procedure. Phenol is rapidly detoxified and eliminated, limiting systemic toxicity following small, localised exposures. The systemic toxicology thresholds reported by ATSDR are exceeded at exposure levels higher than those encountered in controlled podiatric nail surgery (Agency for Toxic Substances and Disease Registry (ATSDR), 2008). Systemic toxicity described in occupational cohorts reflects prolonged exposure and is not directly translatable to the small-volume, localised application used in nail surgery. However, even when corrected, the systemic absorbed dose during nail matrixectomy remains unknown, as key variables (tissue absorption, volatilisation, and procedural loss) are unquantified. Comparisons with tolerable daily intake (TDI) thresholds are methodologically inappropriate without accounting for route-specific pharmacokinetics. Phenol does not accumulate significantly in lipid-rich tissues, suggesting limited long-term retention (Bruce, Santodonato and Neal, 1987). Neither perinatal death rates nor prevalence of malformations were significantly increased in the retrospective study of pregnancy outcome among university laboratory employees in Sweden conducted by Axelsson et al. between infants whose mothers were exposed to solvents and those who were not. (Axelsson, Lutz and Rylander, 1984).
Breastfeeding considerations 
Studies demonstrate detectable phenols in infant urine and breast milk. Neonatal metabolism is immature, particularly with respect to CYP2E1 activity, suggesting reduced capacity to metabolise phenol in early life (Johnsrud, 2003). Evidence on phenol transfer into breast milk is limited, but the authors’ earlier work concluded that, because phenol must cross multiple physiological membranes, phenol-contaminated breast milk is unlikely to affect the baby.

Discussion

Phenol is rapidly absorbed via dermal, inhalational, and oral routes, with systemic effects reported within minutes at high exposure levels. However, it is also rapidly detoxified through hepatic conjugation to sulphate and glucuronide metabolites, which are less toxic and are predominantly excreted in the urine within 24-hours (Bruce, Santodonato and Neal, 1987). Distribution studies demonstrate limited accumulation in lipid-rich tissues, suggesting minimal long-term retention. While high-dose exposure is associated with significant toxicity, the relevance of these findings to podiatric practice is limited, given the small, localised doses used in nail surgery. Much of the phenol toxicology literature is derived from industrial or mixed-exposure models, limiting direct applicability to nail surgery. The key issue is not the total dose applied, but the proportion of phenol that enters the maternal circulation. Current evidence suggests that:
  • Phenol has the potential for systemic toxicity
  • Developmental toxicity occurs at sufficiently high doses
  • Human evidence is inconclusive
Although not clearly teratogenic, phenol is fetotoxic at high doses, supporting cautious use in pregnancy (Bruce, Santodonato and Neal, 1987), although at doses unlikely to be administered during nail surgery. Pregnancy testing is a routine practice for elective surgery (National Institute for Health and Care Excellence (NICE)., 2016). The authors posit that if phenol were especially dangerous to a foetus, pregnancy testing would be mandatory prior to its use. This review identifies a critical limitation in previous work: underestimating phenol exposure due to misinterpretation of units. Our 2022 paper was further limited by its narrative review design, methodological weaknesses, speculative reasoning in parts, and several unsupported clinical recommendations. These issues weaken the strength of its conclusions. Corrected calculations indicate that the procedural phenol load is substantially higher than previously reported. However, the systemic absorption of phenol following nail surgery - and its effect on the foetus - remains unknown.

Conclusion

This paper corrects a previously published underestimation of phenol exposure during matrixectomy and clarifies the distinction between applied and systemic dose, addressing an area of ongoing clinical uncertainty in pregnancy and breastfeeding. While phenol exposure during matrixectomy is higher than previously estimated, the lack of systemic absorption data prevents definitive conclusions about safety. Phenol matrixectomy should therefore be approached with cautious clinical judgement, pending further research. Phenol matrixectomy in pregnancy and breastfeeding should be considered a risk-uncertain intervention. Clinicians should therefore:
  • undertake individualised risk-benefit assessment
  • provide informed consent
  • consider alternative techniques
  • minimise exposure where possible
Future research 
Priority areas include:
  • Biomonitoring studies (urinary phenol pre/post procedure)
  • Pharmacokinetic modelling of dermal absorption
  • Occupational exposure correlation with systemic levels
  • Prospective pregnancy outcome studies

Authors contributions

IR conceived the paper’s aim and format. All authors made substantial contributions to the final version. Authors' information: INR: https://orcid.org/0000-0002-2786-5739.

Funding

this research did not receive any grant from funding agencies in the public, commercial, or not-for-profit sectors.

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Preprints 235132 g001
Figure 1. phenol chemical structure (C₆H₅OH).
Figure 1. phenol chemical structure (C₆H₅OH).
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Figure 2. https://www.dltpodiatry.co.uk/Phenol-Swab-it.
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