Is It Still Dangerous Without Formaldehyde? The Trade-off for Straight Hair: The Frontline of Hair Straightening Ingredients and Health

1) The Assurance of "Formaldehyde-Free" Labels—How Trustworthy Are They?

Formaldehyde (FA) has been used as a preservative and for long-term fixation, but it releases gas when heated, causing strong irritation to the eyes and respiratory tract, worsening asthma, and even posing a cancer risk, leading to regulations in various countries. Consequently, products claiming to be "FA-free" have been marketed as "safer." However, the absence of a label does not mean the absence of risk. The alternative ingredient, glyoxylic acid, presents another health challenge.

2) Key Points of Case Reports in 2025—Who, When, and What Happened?

From April 2021 to March 2025, 13 women aged 15 to 53 were reported to have been transported to medical facilities after feeling unwell following salon treatments. Most exhibited symptoms such as vomiting, abdominal pain, headaches, and rashes 2 to 72 hours post-treatment, with acute kidney injury (AKI) confirmed in 12 cases. Hospitalization lasted 1 to 10 days, with no cases requiring dialysis or resulting in death. Inadequate salon ventilation was noted, and the use of glyoxylic acid-containing products was confirmed during on-site investigations. Notably, one case that sought medical attention within 6 hours and received early administration of vitamin B complex (thiamine = B1, pyridoxine = B6) within 2 hours of hospitalization did not progress to kidney damage.

3) Hypothetical Mechanism—Why Are the Kidneys Targeted?

Glyoxylic acid can be metabolized in the body into oxalate. Excessive oxalate can bind with calcium to form crystals (calcium oxalate), potentially damaging the narrow renal tubules and leading to crystalline nephropathy. The contribution of skin contact, inhalation, and transdermal absorption, as well as the effects of heating and vaporization, remain subjects for future investigation, but consistent findings are emerging with previously reported single and small-scale studies.

4) The Current State of Evidence—Between "Causation" and "Caution"

The case reports are observational, not all cases underwent renal biopsy, and the sample size is not large. Therefore, it is not yet at a stage to declare "definitive causation." However, the temporal proximity, consistency of symptoms, accumulation of previous reports, and validity of metabolic pathways provide a sufficient signal for caution. For healthcare providers, regulatory authorities, the salon industry, and consumers alike, it can be said that "unknown risks are becoming known."

5) The Gap Between Regulation and Practice—Formaldehyde Progresses, Alternative Ingredients Are Untouched

In the United States, a ban proposal targeting formaldehyde and methylene glycol was presented for 2024, but progress towards implementation is stalled in some regions. Meanwhile, states like California and Maryland are advancing FA regulations across cosmetics. However, products labeled "FA-free" containing glyoxylic acid are often not explicitly regulated, with monitoring and information provision lagging. In practice, reliance on manufacturers' training materials and voluntary standards is not uncommon.

6) What Is Happening in Salons—Ventilation, Procedures, and Information Provision

Case reports suggested inadequate ventilation in multiple instances. Since volatile substances are unavoidable during high-temperature ironing or blow-drying, local exhaust and adequate ventilation are essential. Pre-treatment counseling should confirm any history of kidney disease, urinary stones, vitamin deficiency, and dehydration risk, and customers should be informed about ingredients, procedures, and precautions. When using home care products, adhering to temperature, time, and frequency guidelines is crucial.

7) What Is Being Discussed on Social Media—Experts' Warnings and Users' Confusion

On X (formerly Twitter), nephrology experts and academic journal accounts have mentioned the possibility of crystalline nephropathy from glyoxylic acid products, urging caution. On TikTok, public health experts have called for checking ingredient names and considering alternatives. Meanwhile, in Reddit's hair care communities, there are calm observations like "still limited to case levels" and "large-scale studies are needed for causal establishment," alongside practical responses like "avoid for now" and "strictly adhere to ventilation and protocols." Stylists have also voiced that "formaldehyde-free still achieves satisfactory results" and "menu revisions and enhanced information provision are necessary." Overall, a consensus is forming to "make informed choices without excessive fear."

8) What Consumers and Practitioners Can Do Now

• Check Ingredients: Verify the presence of alternative ingredients like "glyoxylic acid."

• Ask the Salon: Inquire about product names, ventilation and local exhaust methods, iron temperature, recommended treatment frequency, and the system for checking medical history.

• Monitor Health Changes: If experiencing vomiting, abdominal pain, reduced urine output, or back pain hours to days after treatment, seek medical attention promptly.

• Hydration and Nutrition: Avoid dehydration, and consult a healthcare provider if extreme vitamin deficiency is suspected.

• Alternative Hair Management: Consider hair dryer technology to reduce heat damage, reassess acid heat treatments, compare with straightening and perming, and utilize styling products.

9) Proposals for Research and Regulation

• Clarify Exposure Routes: Determine the contribution rates of dermal, inhalation, and accidental ingestion, and the decomposition and by-products during heating.

• Diversity in Sensitivity: Investigate the impact of medical history, nutritional status, and genetic predisposition on risk.

• Transparency in Product Information: Standardize ingredients, heating conditions, required ventilation, and treatment protocols.

• Monitoring and Education: Establish a reporting system for adverse events, standardize stylist education, and provide clear information for consumers.

10) Conclusion—Graduating from the "Safety Myth of Labels"

While the absence of formaldehyde is an important step, it does not negate all risks. Internationally accumulating cases suggestive of acute kidney injury with some products containing glyoxylic acid, along with practical issues like ventilation and procedures, are being questioned. Consumers, practitioners, manufacturers, and authorities need to update towards "safer care" based on the latest evidence, which is the shortcut to achieving both straight hair and a healthy body.

※This article is not medical advice. If you have symptoms, please consult a medical institution.