Acute interstitial nephritis with oxalate deposition after hair‑straightening treatment: a case report

Abstract

Background

Acute interstitial nephritis (AIN) is a recognized cause of acute kidney injury (AKI), most commonly associated with medications. Increasing evidence also implicates exposure to environmental chemicals, including hair‑straightening products marketed as “formaldehyde‑free,” which may still contain or release nephrotoxic compounds. Reports have linked these products to oxalate nephropathy that may occur concurrently with interstitial nephritis, underscoring the need for awareness of their renal risks.

Case presentation

We describe a 26-year-old healthy woman who presented with nausea, vomiting, and bilateral flank pain three days after undergoing a professional hair-straightening treatment. Laboratory investigations revealed Stage 3 AKI with serum creatinine level 372 µmol/L, while serologic and infectious workup was unremarkable. Urinalysis showed leukocyturia, hematuria, and proteinuria. Kidney ultrasound was normal. Shortly after product application, the patient had experienced scalp pruritus and erythema. Kidney biopsy demonstrated mild mixed interstitial infiltrates with eosinophils, tubulitis, and rare intratubular oxalate crystals, consistent with acute hypersensitivity interstitial nephritis. Treatment with intravenous methylprednisolone followed by oral prednisolone resulted in clinical improvement and normalization of renal function within one month. Product review identified glycolic acid, a compound metabolized to oxalate, as a potential etiological factor.

Conclusion

This case illustrates severe AKI due to AIN with oxalate deposition following exposure to a hair-straightening product marketed as FA-free. Clinicians should maintain high suspicion for cosmetic exposures in patients with unexplained AKI. Awareness of these potential nephrotoxic effects is essential to support early recognition, appropriate management, and preventive public health measures.

Background

Acute interstitial nephritis (AIN) is a well-established cause of acute kidney injury (AKI). Medications, particularly antibiotics, non-steroidal anti-inflammatory drugs, and proton pump inhibitors, are among the most frequently reported causes [1, 2]. Emerging evidence, however, indicates that exposure to environmental chemicals may also play a role in its pathogenesis [3–5]. In this context, hair-straightening treatments, which have gained popularity among both women and men in recent years, have raised concern due to limited awareness of their potential systemic toxicities and associated chemical exposures [6, 7]. These products are cosmetic preparations rather than medications, although their chemical constituents may still have systemic toxicological effects.

Observational studies have highlighted the adverse health effects of chemically based hair treatments, with AKI reported after hair-straightening procedures, ranging from mild renal impairment to severe presentations requiring renal replacement therapy [8], accompanied by heterogeneous histopathological findings.

Formaldehyde (FA) and FA-releasing compounds, such as methylene glycol, were among the first harmful ingredients identified in hair-straightening products [9]. FA exposure has been linked to adverse health effects, including AKI [10, 11]. Products marketed as “formaldehyde-free” may still release FA or related compounds when heated [12, 13], and one review detected FA in 8% of such products [14].

Abu-Amer et al. described a case of stage III AKI, classified according to the Kidney Disease: Improving Global Outcomes (KDIGO) criteria, following exposure to a hair-straightening product marketed as FA-free. Kidney biopsy demonstrated acute tubular necrosis with tubulointerstitial nephritis and oxalate deposition [12]. Oxalate nephropathy may result from absorption of glyoxylic acid through the scalp, which is subsequently metabolized to oxalic acid [15]. Bnaya et al. further reported 26 patients with severe AKI after hair straightening, in whom acute oxalate nephropathy was the predominant lesion, likely due to absorption of glycolic acid derivatives and subsequent oxalate formation [6]. A similar case implicated glyoxylic acid in Brazilian hair-straightening products, with recurrent AKI and biopsy findings of interstitial nephritis and oxalate crystals [7]. In animal models, exposure to glyoxylic acid–containing products led to oxalate crystalluria, renal oxalate deposition, and elevated serum creatinine levels, changes absent in controls [16].

These cases stress the probable nephrotoxic effects of hair straightening products, even those advertised as FA-free. Given the extensive use of said treatments, it is essential to consider them in the differential diagnosis of unexplained AKI and to raise awareness among healthcare providers and consumers about their possible renal effects.

Case presentation

This case is presented to highlight the importance of comprehensive history taking, early recognition of the etiology of AKI, and prompt management.

A 26-year-old female medically free presented to the emergency department with nausea, vomiting and bilateral flank pain. The symptoms began three days earlier without a clearly identifiable preceding event, and there was no reported use of herbal remedies, new medications, or illicit drugs. On Physical examination, her vital signs revealed heart rate 95 bpm and blood pressure 102/56 mmHg; she had no fever, respiratory distress or skin eruption. There were moderate dehydration and mild abdominal tenderness. Laboratory investigations revealed a serum creatinine level of 372 µmol/L (baseline 60 µmol/L), urea 8.5 mmol/L, potassium 4.1 mmol/L, sodium 134 mmol/L, chloride 97 mmol/L, and bicarbonate 24.3 mmol/L.

Complete blood count, liver function tests, β-hCG, serum albumin, and other electrolytes were within normal limits. Urinalysis, including microscopic examination, demonstrated leukocytes (3–6 / HPF) and microscopic hematuria (1–3 / HPF). The urine protein-creatinine ratio was 33.5 mg/mmol, and urine culture was negative. (Table 1)

Table 1.

Complete blood count (CBC) and serum chemistry results

Test	Specimen	Result	Reference Range
WBC	Blood	9.88 × 10³/µL	3.8–11.0 × 10³/µL
RBC	Blood	4.54 × 10⁶/µL	4.30–5.80 × 10⁶/µL
Hemoglobin	Blood	11.0 g/dL	13.0–18.0 g/dL
Hematocrit	Blood	34.6%	40–52%
Platelet count	Blood	308 × 10³/µL	140–440 × 10³/µL
Serum creatinine	Blood	372 µmol/L	44–80 µmol/L
BUN	Blood	8.5 mmol/L	4.2–7.2 mmol/L
Sodium	Blood	134 mmol/L	135–148 mmol/L
Potassium	Blood	4.4 mmol/L	3.5–5.1 mmol/L
Chloride	Blood	97 mmol/L	98–108 mmol/L
Bicarbonate (CO₂)	Blood	24.3 mmol/L	23–30 mmol/L
Magnesium	Blood	0.66 mg/dL	1.6–2.3 mg/dL
Phosphorus	Blood	1.55 mg/dL	2.5–4.5 mg/dL
Albumin	Blood	30 g/L	35–50 g/L
ALT	Blood	45 U/L	7–56 U/L
AST	Blood	30 U/L	10–40 U/L
Total bilirubin	Blood	0.5 mg/dL	0.1–1.2 mg/dL
β-hCG	Blood	< 2 IU/L	< 2 IU/L
Protein/creatinine ratio	Urine	33.5 mg/mmol	15–50 mg/mmol
Glucose	Urine	Negative	Negative
Protein	Urine	Negative	Negative
Blood	Urine	Negative	Negative
Ketones	Urine	Trace	Negative
Nitrite	Urine	Negative	Negative
Leukocytes	Urine	Trace	Negative
pH	Urine	6.0	5–9
Specific gravity	Urine	1.010	1.005–1.030
WBC (microscopy)	Urine	3–6 / HPF	0–5 / HPF
RBC (microscopy)	Urine	1–3 / HPF	0–5 / HPF
Epithelial cells	Urine	Many	None

Abbreviations: WBC, white blood cells; RBC, red blood cells; BUN, blood urea nitrogen; ALT, alanine aminotransferase; AST, aspartate aminotransferase; β-hCG, beta-human chorionic gonadotropin; HPF, high-power field

Ultrasound revealed normal size kidneys, normal echogenicity and preserved cortico-medullary differentiation and no stones.

Serology for human immunodeficiency virus (HIV), hepatitis B, hepatitis C, hepatitis A, antinuclear antibody (ANA), antineutrophil cytoplasmic antibodies (ANCA), and anti-glomerular basement membrane (anti-GBM) antibodies were negative. Complement C3 and C4 levels were within the normal range.

On the first day of hospitalization, the patient’s urine output remained within normal limits; however, her serum creatinine levels continued to rise despite adequate hydration. The patient reported undergoing a hair-straightening procedure at a professional beauty salon. Shortly after application of the product, she experienced intense scalp pruritus, and erythema. The product was left on her hair for approximately 50 min. She noted having undergone similar hair treatments for many years without incident, making this the first occurrence of such symptoms.

On the second day of hospitalization, a native kidney biopsy was performed, 5 intact glomeruli were examined. The biopsy demonstrated mild mixed interstitial inflammatory infiltrates composed predominantly of lymphocytes with scattered eosinophils and occasional plasma cells, associated with mild tubulitis. (Figures 1 and 2) and rare intratubular oxalate crystals in keeping with acute hypersensitivity interstitial nephritis (Fig. 3).

Fig. 1.

Portion of cortical tissue showing mixed interstitial inflammation (H&E, 20x)

Fig. 2.

Fan-like translucent calcium oxalate crystal within the tubular lumen (H&E, 40x) (Black arrow)

Fig. 3.

Birefringent calcium oxalate crystal under polarized light (60x)

Following the diagnosis of acute hypersensitivity interstitial nephritis, the patient was treated with pulse methylprednisolone 250 mg intravenously for 3 days, followed by oral prednisolone at 1 mg/kg for 2 weeks, which was tapered over the subsequent 3 weeks. Given the presence of oxalate crystals on kidney biopsy, a detailed dietary recall was undertaken. The patient denied adherence to a deliberately high-oxalate diet and reported no use of vitamin C supplements. She described only intermittent consumption of homemade “green juices” prepared with celery, spinach, apples, and oranges, typically one to two servings per month, each approximately 250–300 ml. Her daily diet otherwise consisted of traditional Saudi foods, characterized by rice-based dishes, wheat-based foods, and meat-focused meals, with some overlap with Mediterranean dietary components. She also denied a history of nephrolithiasis, and renal ultrasonography confirmed the absence of kidney stones.

The patient was discharged from the hospital on day four. At the one-month outpatient follow-up, the patient’s serum creatinine level had normalized to 73 µmol/L.

Patient perspective of her condition and diagnosis

I would like to express my sincere gratitude to the medical team for their thorough investigation to identify the cause of my kidney injury. Their daily rounds and clear explanations about my condition and the possible causative agents were greatly appreciated. I am thankful for my treating doctor for her ongoing care in the outpatient clinic until my kidney function returned to normal. I also look forward to the team sharing the paper with me once it is published.

Discussion

This case highlights an uncommon but clinically important cause of acute interstitial nephritis with oxalate deposition following exposure to a cosmetic hair‑straightening product. Recent literature increasingly links these cosmetic formulations—particularly those containing glyoxylic or glycolic acid derivatives—to acute kidney injury. Recognition of cosmetic exposures is therefore essential when evaluating patients with otherwise unexplained acute kidney injury.

A review of the literature identified several reports of AKI following exposure to hair-straightening products marketed as FA-free. Notably, all cases were published after 2019, with the first reported in Iran [17]. To the best of our knowledge, this is the first such case reported from Saudi Arabia.

Our patient presented with stage 3 AKI following exposure to a hair-straightening product marketed as FA-free. Other common causes of AKI, including acute illness (such as severe infection, dehydration, or systemic inflammatory conditions), drug toxicity, herbal use, and exposure to known nephrotoxic agents, were excluded. Kidney biopsy demonstrated mild mixed interstitial inflammatory infiltrates composed predominantly of lymphocytes with eosinophils and mild tubulitis, together with rare intratubular oxalate crystals, consistent with acute hypersensitivity interstitial nephritis. We speculate that both the clinical presentation and histopathologic findings were directly attributable to this exposure. The onset of nausea, vomiting, and severe scalp irritation shortly after treatment strongly suggests chemical intoxication, particularly in the absence of alternative explanations. The close temporal relationship between product exposure and symptom onset, together with the exclusion of other common causes of acute kidney injury, supports a likely causal association between the hair-straightening product and the observed renal injury. In most reported cases, symptoms developed within 48 h of exposure [8].

A detailed review of the product used in this case revealed the presence of ethylhexyl glycerin, propylene glycol, and glycolic acid. Of these, only glycolic acid has previously been implicated in AKI. Another component identified was propylene glycol, a solvent commonly used in cosmetic formulations and occasionally in pharmaceutical preparations. Although uncommon, propylene glycol has been reported to cause AKI. In one report [18], the suggested pathology was proximal tubular renal cell injury associated with a markedly elevated osmolar gap and high anion gap metabolic acidosis due to lactic acidosis. Nonetheless, our patient demonstrated a normal anion gap and normal lactic acid levels [19].

Glycolic acid and its derivatives are widely used in cosmetic formulations, including hair-straightening treatments. Although generally considered safe for topical application, absorption depends on concentration and duration of exposure, particularly when the skin barrier is compromised. Some data suggest it may act as an irritant, but no significant association with direct kidney injury has been reported [20]. Notably, when heated during the straightening process, glycolic acid can behave as an aldehyde and generate toxic formaldehyde gas.

FA is a colorless, toxic aldehyde that exists as a gas at room temperature. In the kidney, formaldehyde has been reported to exert direct cytotoxic effects, leading to acute toxic tubular necrosis. Some evidence also suggests it may contribute to acute interstitial nephritis [17].

The net result of glycolic acid metabolism is oxalate. A finding was likewise present in our patient. (Fig. 3). Deposition of calcium oxalate crystals within renal tubules can cause acute or chronic decline in kidney function [21]. A Belgian study reported a prevalence of up to 1% among native kidney biopsies, while another study by Yang Y, Sharma PD, et al. estimated the prevalence in the general population to be as high as 4% [21, 22]. Acute oxalate nephropathy is a rare disorder that can occur due to high oxalate load (i.e., vitamin C consumption or ethylene glycol ingestion). Kidney impairment due to oxalosis has been described in approximately 1% of kidney biopsies in a study from the UCLouvain Kidney Disease Network. Among these cases, 85% showed features AIN, similar to our patient [23]. When oxalate nephropathy is identified on kidney biopsy, a comprehensive evaluation for excessive dietary oxalate intake and potential enteric hyperoxaluria is warranted, particularly in the context of chronic diarrhea, as these factors may contribute to stone formation and oxalate-mediated renal injury [24, 25]. As outlined in the case presentation, the patient’s green-juice intake was infrequent and modest, representing a level of exposure that may be considerably lower than the quantities associated with diet-induced hyperoxaluria in individuals without predisposing enteric conditions [26–28]. The traditional Saudi dietary pattern, composed largely of rice-based dishes, wheat-based foods, and meat-focused meals, is not considered a significant source of dietary oxalate and would not be expected to substantially increase overall oxalate burden, based on published oxalate content analyses [29]. Similarly, the Mediterranean diet is not intrinsically high in oxalate and has been associated with a lower risk of nephrolithiasis in population studies [25]. Given the widespread use of cosmetic hair-straightening products globally, clinicians should consider recent cosmetic exposures when evaluating patients presenting with unexplained acute kidney injury. Taken together, the absence of recognized dietary or enteric contributors to hyperoxaluria in this patient strengthens the plausibility that her oxalate nephropathy was secondary to glycolic acid exposure from the hair-straightening product.

Lastly, while FA cannot be excluded as a potential nephrotoxic contributor to AKI in our patient, the presence of calcium oxalate deposits in kidney biopsy specimens suggests that metabolism of glycolic acid derivatives to oxalate was the primary mechanism of nephrotoxicity [6].

Conclusions

In conclusion, we report a case of severe AKI following exposure to a FA-free hair-straightening treatment. This case highlights the kidney’s sensitivity to exposure to environmental chemicals and underscores the importance of raising awareness about the potential risks of widely used cosmetic products. Further studies are warranted to better elucidate the underlying pathophysiological mechanisms and to develop strategies aimed at preventing such potentially catastrophic kidney injury.

Abbreviations

AIN

Acute interstitial nephritis

AKI

Acute kidney injury

ANA

Antinuclear antibody

anti‑GBM

Anti‑glomerular basement membrane

FA

Formaldehyde

KDIGO

Kidney Disease: Improving Global Outcomes

Author contributions

M.A.K.: Conceptualization; Investigation; Data curation; Visualization; Writing – original draft. F.N.Y.: Conceptualization; Methodology; Supervision; Project administration; Writing – review & editing; Corresponding author. R.A.A.: Investigation; Data curation; Visualization (Table 1); Writing – review & editing. G.A.M.: Validation; Investigation (pathology); Visualization (Figs.  1, 2 and 3); Writing – review & editing (figure legends). F.C.: Supervision; Resources; Writing – review & editing.All authors read and approved the final manuscript.

Funding

This research received no external funding.

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethical approval

Ethics approval was obtained from the Institutional Review Board of King Faisal Specialist Hospital & Research Centre (KFSH&RC-IRB) (Approval No. 2255971; issued on October 26, 2025). Written informed consent was obtained from the patient prior to participation. A copy of the informed consent form is provided at the end of the manuscript.

Consent for publication

Written informed consent for publication of this case report and any accompanying images was obtained from the patient. A copy of the consent form is available for review by the Editor of this journal.

Competing interests

The authors declare no competing interests.