Titanium Dioxide and Cancer

Titanium dioxide is a bright white powder. Its chemical formula is TiO2. Safety sheets list it under CAS number 13463-67-7. It scatters light better than almost any other cheap solid. A small amount makes a product look opaque and very white. That is why it shows up in paint, plastic, paper, ink, and toothpaste. It is also in some sunscreens and in the white coating on some candies and pills.

Two things decide whether any of that matters for cancer risk. The first is the physical form. A fine dust floating in the air acts nothing like the same pigment locked inside dried paint. The second is the route into the body. Breathing a dust is not the same as rubbing a cream on your arm. It is not the same as swallowing a trace amount in frosting.

The International Agency for Research on Cancer (IARC) is the cancer research arm of the World Health Organization. It reviews substances in working groups. Each group of agents gets its own published volume. TiO2 was reviewed in Volume 93, published in 2010, alongside carbon black and talc.

The working group wrote three separate findings. On people: "There is inadequate evidence in humans for the carcinogenicity of titanium dioxide." On animals: "There is sufficient evidence in experimental animals for the carcinogenicity of titanium dioxide." The overall call: "Titanium dioxide is possibly carcinogenic to humans (Group 2B)."

Group 2B is the weakest positive box IARC uses. "Inadequate evidence" does not mean the studies found safety. It means the human studies were too few, or too mixed, to settle the question either way.

The human studies were real but thin. One multi-country study of TiO2 plant workers was called the single most useful one. It found a slightly higher rate of lung cancer than in the general public. The pattern hinted at a dose-response. It found no overall excess of kidney cancer. Two other worker studies found no raised risk. A case-control study found none either. That mix is why the human evidence was graded inadequate.

The animal side was more consistent. Two studies had rats breathe the powder. One found extra lung tumors in both sexes, the other in females only. Rats given the powder straight into the windpipe also grew more lung tumors. Mice and hamsters treated the same way did not. Other routes of exposure showed nothing.

There is a name for the pattern behind this: particle overload. Load a rat lung heavily with almost any dust that will not dissolve, and the cells that clear debris fall behind. Long-running swelling follows, and tumors can follow that. IARC put carbon black, TiO2 and talc in one volume for that reason. All three are poorly soluble particles that are only weakly toxic on their own. The open question was whether the rat lung story carries over to people in dusty trades, such as coal mining. On TiO2 the group found that the mechanism evidence "was not strong enough to warrant a classification other than Group 2B."

If you handle this powder for a living, two federal numbers apply. They are far apart.

• OSHA sets a legal permissible exposure limit (PEL), the most a worker may breathe on average across a shift. For TiO2 as total dust it is 15 milligrams per cubic meter of air.
• NIOSH is the federal research institute for job safety. It recommends much lower ceilings: 2.4 mg/m3 for fine TiO2 and 0.3 mg/m3 for the ultrafine grade. NIOSH also flags it as a possible job-related carcinogen.

Both sit side by side in OSHA's annotated Table Z-1. The gap is not a contradiction. The OSHA figure is the rule an inspector can enforce. The NIOSH figures are advice from a later look at the same overload evidence. They are also the ones that treat the ultrafine grade as its own problem. Control is ordinary industrial hygiene. That means closed transfer of powder, exhaust hoods at bagging and mixing points, wet cleanup instead of dry sweeping, and fit-tested respirators where dust cannot be engineered away.

Nothing in the 2010 review rested on skin contact. Mineral sunscreens use TiO2 because it sits on the skin surface and scatters ultraviolet light. Skin is not lung tissue, and a cream is not an airborne dust. The one product format where breathing is even plausible is a loose powder or a spray. Those are worth pointing away from your face as you apply them. If you are weighing sun safety against chemical worry, our page on sunscreen covers what these products do and do not do.

Food is governed by a specific rule rather than a general opinion. In the United States, TiO2 is a color additive listed at 21 CFR 73.575. The rule caps how much may be used. The quantity "does not exceed 1 percent by weight of the food." It also sets purity limits the pigment must meet. Those include at least 99.0 percent TiO2 after drying, lead no higher than 10 parts per million, arsenic and mercury no higher than 1 part per million each, and antimony no higher than 2 parts per million. Other countries have made different calls on food use. That is why headlines from Europe and the United States can disagree while both describe real rules.

One more piece of context. The National Toxicology Program's 15th Report on Carcinogens names a list of substances known to be human carcinogens. TiO2 is not on that list.

A carcinogen listing answers a narrow question. Can this substance cause cancer under some conditions? It does not answer how likely cancer is for you at the exposure you actually have. Those are two different questions. Our page on hazard versus risk works through why a Group 2B listing and a personal risk estimate are not the same thing. If you want the general framework first, start with what a carcinogen is.

For TiO2, the honest summary is short. The exposure that earned the listing is years of breathing fine powder, mostly at work, at levels no shopper meets. The consumer exposures were not the basis of the finding. That includes paint on a wall, pigment in a plastic chair, a mineral sunscreen, and a trace in a coated candy. If you work with the powder, the dust controls and the NIOSH numbers are where your attention belongs.

• IARC Monographs Volume 93 — Carbon Black, Titanium Dioxide, and Talc (2010)
• IARC Monographs Volume 93, full text on NCBI Bookshelf
• 21 CFR 73.575 — Titanium dioxide (govinfo)
• OSHA Annotated Permissible Exposure Limits, Table Z-1
• NCI — Cancer-Causing Substances in the Environment