Is Sodium Lauryl Sulfate (SLS) in Toothpaste Safe?

Just because the sodium lauryl sulfate in toothpaste doesn’t cause cancer doesn’t mean it can’t cause problems.

Sodium lauryl sulfate (SLS) is a common detergent used in toothpaste. It was featured in a famous Internet hoax nearly 20 years ago. Colgate toothpaste contains SLS, which was supposedly proven to cause cancer, but at least buying Colgate rather than Crest, manufactured by Procter & Gamble, didn’t support Satan—or so claimed another famous hoax that alleged that “a large portion of the profits of Procter and Gamble products goes to support the Satanic Church.”

The hoax that SLS in toothpaste and hair care products was linked to cancer became so widespread the American Cancer Society was forced to publish a response to shampoo-poo the link. Read the organization’s “Debunking the Myth” article, “Radical chain e-mails have been flying through cyberspace stating Sodium Lauryl Sulfate or SLS, a common ingredient in many health and beauty aids, is known to cause cancer. This is not true, according to researchers.” So, I just ignored it all these years, until I was doing research on canker sores, those painful, shallow, gray ulcerations you can get inside your lip or cheek, also known as aphthous ulcers. They can often be set off by trauma, like when you accidentally stab yourself with a toothbrush, so it’s recommended to try not to bite your lip and to avoid SLS-containing toothpaste—not because of cancer, but because of irritation. That at least makes a little more sense. Why would a detergent, a soap chemical, be carcinogenic? Though, you could imagine how SLS, theoretically, could at least dissolve some of the protective layer from the inside of your mouth. So, I decided to look into it, as I discuss in my video Is Sodium Lauryl Sulfate Safe?.

Although SLS has been used as a foaming agent in toothpastes since the 1930s, our story begins 25 years ago with an abstract presented at a conference on the possible effects of SLS on recurrent canker sores. Researchers took ten men and women getting more than one sore a week, nearly 18 on average over a three-month period, who had been using a regular SLS-containing toothpaste, and switched them to an SLS-free toothpaste for another three months. The subjects went from 18 canker sores down to around 5—about a 70 percent decrease. The researchers thought the SLS was adversely affecting the protective mucus layer that lines the mouth.

You always have to be cautious about published abstracts, though. You should always make sure that researchers actually go on to publish their findings in a peer-reviewed medical journal. And, indeed, in this case, they did. So we can confirm they conducted a double-blind study and used the same toothpaste, one with the regular concentration of SLS and the other SLS-free, but still with just ten patients. Though it was considered a preliminary study, it apparently had such a dramatic effect that a series of experiments were performed to see what might be going on. Researchers simply applied some SLS at the concentration found in toothpaste onto someone’s gums with a Q-tip for 90 seconds and measured the spike in blood flow to the area, a sign of inflammation, presumably because the detergent was penetrating and irritating the gums, as you can see at 3:06 in my video. But does it actually damage the tissue?

Researchers smeared some toothpastes on the gums of some dental hygienists for two minutes twice a day for four days, and although the SLS-free toothpaste didn’t cause any problems, the ones with the typical amount of SLS caused “desquamation” among most of the participants—in other words, a sloughing off or peeling of the topmost layers of the inside lining of their mouths. No wonder SLS might make canker sores worse.

If you go back to the original American Cancer Society source debunking SLS as being cancer-causing, the response was that SLS is not a known carcinogen—it’s just a known irritant.

What about the non-SLS foaming agents? I discuss them in my video Is CABP in SLS-Free Toothpaste Any Better?.


I’ve taken a deep dive into canker sores. See, for example:

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations:

The Difference Between Alpha and Beta Receptors Explain Soy’s Benefits

“[S]oyfoods have become controversial in recent years…even among health professionals…exacerbated by misinformation found on the Internet.” Chief among the misconceptions is that soy foods promote breast cancer because they contain a class of phytoestrogen compounds called isoflavones, as I explore in my video, Is Soy Healthy for Breast Cancer Survivors? Since estrogens can promote breast cancer growth, it is natural to assume that phytoestrogens might, too, but most people do not realize there are two different types of estrogen receptors in the body, alpha and beta. Unlike actual estrogen, soy phytoestrogens “preferentially bind to and activate ERβ,” estrogen receptor beta. “This distinction is important because the [two types of receptors] have different tissue distributions within the body and often function differently, and sometimes in opposite ways. This appears to be the case in the breast,” where beta activation has an anti-estrogenic effect, inhibiting the growth-promoting effects of actual estrogen—something we’ve known for more than ten years.

The effects of estradiol, the primary human estrogen, on breast cells are “completely opposite” to those of soy phytoestrogens, which have “antiproliferative effects on breast cancer cells…even at [the] low concentrations” we get in our bloodstream after eating just a few servings of soy. This makes sense, given that after eating a cup of soybeans, the levels in our blood cause significant beta receptor activation, as you can see at 1:27 in my video.

Where did this outdated notion that soy could increase breast cancer risk come from? The concern was based largely on research that showed that the main soy phytoestrogen, genistein, stimulates the growth of mammary tumors in a type of mouse—but, it turns out, we’re not mice. We metabolize soy isoflavones very differently from rodents. As you can see at 2:00 in my video, the same soy phytoestrogens led to 20 to 150 times higher levels in the bloodstream of rodents. The breast cancer mouse in question had 58 times higher levels. What does this mean for us? If we ate 58 cups of soybeans a day, we could get some significant alpha activation, too, but, thankfully, we’re not hairless athymic ovariectomized mice and we don’t tend to eat 58 cups of soybeans a day.

At just a few servings of soy a day, with the excess beta activation, we would assume soy would actively help prevent breast cancer. And, indeed, “[s]oy intake during childhood, adolescence, and adult life were each associated with a decreased risk of breast cancer.” Those women who ate the most soy in their youth appeared to grow up to have less than half the risk. This may help explain why breast cancer rates are so much higher in the United States than in Asia, where soy foods are more commonly consumed. Yet, when Asians come to the United States and start eating and living like Americans, their breast cancer risk shoots right up. Women in their 50s living in Connecticut, for example, are way at the top of the breast cancer risk heap, as you can see at 3:00 in my video, and have approximately ten times more breast cancer than women in their 50s living in Japan. It isn’t genetic, however. When Japanese women move to the United States, their breast cancer rates go up generation after generation as they assimilate into American culture.

Are the anti-estrogenic effects of soy foods enough to actually change the course of the disease? We didn’t know until the first human study on soy food intake and breast cancer survival was published in 2009 in the Journal of the American Medical Association, suggesting that “[a]mong women with breast cancer, soy food consumption was significantly associated with decreased risk of death and [breast cancer] recurrence.” That study was followed by another study, and then another, each with similar findings. That was enough for the American Cancer Society, which brought together a wide range of cancer experts to offer nutrition guidelines for cancer survivors, concluding that, if anything, soy foods should be beneficial. Since then, two additional studies have been published for a total of five—five out of five studies that tracked more than 10,000 breast cancer patients—and they all point in the same direction.

Pooling all of the results, soy food intake after breast cancer diagnosis was associated with both reduced mortality and reduced recurrence—that is, a longer lifespan and less likelihood that the cancer comes back. This improved survival was for women with estrogen receptor negative tumors and estrogen receptor positive tumors, and for both younger women and for older women.

Pass the edamame.


Flaxseeds are protective for likely the same reasons. For more on this, see my videos Flaxseeds and Breast Cancer Survival: Epidemiological Evidence and Flaxseeds and Breast Cancer Survival: Clinical Evidence.

What about women who carry breast cancer genes? I touched on that in BRCA Breast Cancer Genes and Soy and Should Women at High Risk for Breast Cancer Avoid Soy?.

What about genetically modified soy? See GMO Soy and Breast Cancer.

Who Shouldn’t Eat Soy? An excellent question I answer in that video.

For even more information on soy, see:

Not all phytoestrogens may be protective, though. See The Most Potent Phytoestrogen Is in Beer and What Are the Effects of the Hops Phytoestrogen in Beer?.

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations:

The Best Source of Vitamin D

If one is going to make an evolutionary argument for what a “natural” vitamin D level may be, how about getting vitamin D in the way nature intended—that is, from the sun instead of supplements? I run through the pros and cons in my video The Best Way to Get Vitamin D: Sun, Supplements, or Salons?. Though supplements may only cost about 10 dollars a year, sunlight is free. We never have to worry about getting too much vitamin D from sunlight, since our body has a way to regulate production in the skin, so if we get our D from the sun, we don’t have to trust poorly regulated supplement companies not to mislabel their products. Indeed, only about half the supplement brands that researchers tested came within 10 percent of their labeled amount.

Sunlight may also have benefits beyond vitamin D, such as how our body may use the sun’s near-infra-red rays that penetrate our skin to activate chlorophyll by-products in our bloodstream to make Co-Q10. (See my video How to Regenerate Coenzyme Q10 (CoQ10) Naturally for more on this.) There’s another way our body appears to use the sun’s rays to maximize the effects of the greens we eat: Within 30 minutes of exposure to the ultraviolet (UV) rays in sunlight, we can get a significant drop in blood pressure and improvement in artery function, thanks to a burst of nitric oxide-releasing compounds that flow into our bloodstream. We can even measure the nitric oxide gas coming straight off our skin. Of course, we have to eat greens or beets in the first place, but that combo of greens and sunlight may help explain some of the protection that plant-based eaters experience.

Morning sun exposure may help those with seasonal affective disorder, as well as improve the mood of wheelchair-bound nursing home residents. Previously, I’ve talked about the benefits of avoiding light at night—see my video Melatonin and Breast Cancer if you’d like to know more—but underexposure to daytime sunlight may also affect our melatonin levels, which don’t only regulate our circadian rhythms but may also be helpful in the prevention of cancer and other diseases. Older men and women getting two hours of outside light during the day appear to secrete 13 percent more melatonin at night, though we’re not sure what, if any, clinical significance this has.

The downsides of sun exposure include increased risk of cataracts, a leading cause of vision loss, though this risk can be minimized by wearing a brimmed hat and sunglasses. Sunlight also ages our skin. In my The Best Way to Get Vitamin D: Sun, Supplements, or Salons? video, you can see a dramatic photo of a truck driver who spent decades getting more sun on the left side of his face—though his driver’s side window. “The effects of sunlight on the skin are profound, and are estimated to account for up to 90% of visible skin aging”—that is, wrinkles, thickening, and loss of elasticity. Things like sun exposure and smoking can make us look 11 years older. Cosmetic surgery can make us look up to eight years younger, but a healthy lifestyle may work even better. Doctors don’t preach about sun protection for youthful facial looks, though, but because of skin cancer. Medical authorities from the World Health Organization, the American Cancer Society, to the Surgeon General warn about excess sun exposure and for good reason, given the millions of skin cancers and thousands of deaths diagnosed every year in the United States alone.

The UV rays in sunlight are considered a complete carcinogen, meaning they can not only initiate cancer, but promote its progression and spread. Melanoma is the scariest, which “makes the rising incidence of melanoma in young women particularly alarming.” This increase has been blamed on the increased usage of tanning salons. Tanning beds and UV rays in general are considered class 1 carcinogens, like processed meat, accounting for as many as three quarters of melanoma cases among young people and six times the risk of melanoma for those who visited tanning salons ten or more times before the age of 30.

The tanning industry is big business, bringing in billions of dollars. There may be more tanning salons than there are Starbucks, and they use those dollars like the tobacco industry: to downplay the risks of their products. Laws are being passed to regulate tanning salons, from complete prohibitions, like in the country of Brazil, to age restrictions for minors. But, unlike tobacco, tanning isn’t addictive. Or is it?

Have you heard of “tanorexia”? Some people tan compulsively and report a so-called tanner’s high. Describing tanning behavior like a substance abuse disorder might seem a little silly—that is, until you stick people in a brain scanner and can show the same kind of reward pathways light up in the brain, thanks to endorphins that are released by our skin when we’re exposed to UV rays. In fact, we can even induce withdrawal-like symptoms by giving tanners opiate-blocking drugs. So, tanning is potentially addictive and dangerous. Harvard researchers suggest that we should “view recreational tanning and opioid drug abuse as engaging in the same biological pathway.” But there’s a reason sun exposure feels good. Sunlight is the primary natural source of vitamin D, and, evolutionarily, it’s more important, in terms of passing along our genes, not to die of rickets in childhood. Unlike natural sunlight, tanning bed lights emit mostly UVA, which is the worst of both worlds: cancer risk with no vitamin D production. The small amount of UVB many tanning beds do emit, however, may be enough to raise vitamin D levels. Is there a way to raise D levels without risking cancer? Yes: vitamin D supplements.


Indeed, we can get some of the benefits of sun exposure without the risks by taking vitamin D supplements. But, for the sake of argument, what if such supplements didn’t exist? Would the benefits of sun exposure outweigh the risks? That’s the subject of my video The Risks and Benefits of Sensible Sun Exposure.

For other videos in this vitamin D series, see:

I also explore Vitamin D as it relates to specific diseases:

Here’s the video about that amazing chlorophyll activation: How to Regenerate Coenzyme Q10 (CoQ10) Naturally.

What do greens and beets have to do with artery function? Check out some of my latest videos on the wonders of nitrate-rich vegetables:

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations: