Chemical Additives in Toothbrush Bristles
Comparing Colgate and Oral-B bristles by LC-MS
The suspected carcinogen anthraquinone showed up at its highest level in the electric Oral-B sample (p = 0.044), even though the two brands were otherwise chemically near-identical.
Objective
Plastic toothbrushes get thrown out by the millions, yet almost nobody knows what’s actually in the bristles. This project asked a narrow, testable version of that question: do the chemical additives in toothbrush bristles differ between the two biggest brands? I compared a manual Colgate (Sample A), a manual Oral-B (Sample B), and an electric Oral-B (Sample C), and went in expecting Colgate to carry more additives at higher concentrations.
Approach
Three replicates of roughly 0.1 g of white bristles came off each toothbrush, controlling for bristle color and type so dye chemistry wouldn’t muddy the comparison. Samples A and C were boiled to sterilize; B was washed but not boiled. Each replicate got 1 mL of acetonitrile, two minutes of vortexing, and a careful supernatant transfer so only dissolved compounds reached the instrument. Everything ran on liquid chromatography-mass spectrometry (LC-MS). Acetonitrile-only procedure blanks were subtracted to strip out solvent and equipment background, and two-tailed t-tests compared each sample against the blanks and the brands against each other.
Findings
Four compounds turned up across the samples: linopirdine, guaiactamine, troxipide, and anthraquinone. Three of them showed no significant difference between brands (p > 0.05), which points to incidental contamination from shared supply chains rather than deliberate additives. Anthraquinone was the exception. It peaked in Sample C, the electric Oral-B, and was the only compound to clear significance against the blank (p = 0.044). That matters because anthraquinone is a suspected carcinogen flagged by the National Toxicology Program, and its pattern is consistent with an antimicrobial coating. The clustered heatmap tells the broader story: the columns look alike, so the chemistry is largely uniform across both brands.
Why it matters
The hypothesis didn’t hold. Colgate and Oral-B came out chemically near-identical, which suggests common materials and manufacturing across the industry. The real signal isn’t brand difference, it’s that a suspected carcinogen sits in a product people put in their mouths daily, undisclosed. Boiling likely leached out some signal, so these numbers are a floor, not a ceiling. The honest takeaway is a case for more transparency in what goes into everyday plastic goods, and for biodegradable alternatives that still need this same screening.