Sodium lauryl sulfate (SLS) is a chemical compound found in thousands of everyday products, from toothpaste and shampoo to laundry detergent and dish soap. It is a surfactant, meaning it lowers the surface tension between ingredients, allowing them to mix and creating that foamy, bubbly lather people associate with cleaning. While it is highly effective at its job, SLS has also been the subject of persistent rumors and online health concerns. The reality is that SLS is safe at the levels used in consumer products, though it can cause skin irritation for some people.
What Is Sodium Lauryl Sulfate and How Does It Work?
SLS is a detergent and foaming agent. It is derived from petroleum or plant-based sources like coconut oil. In a product, its job is to bind with both water and oil. This unique property allows it to lift dirt, grease, and debris off your skin, hair, or dishes so they can be rinsed away.
This mechanism is why your shampoo lathers and why your toothpaste foams. The bubbles are not necessary for cleaning, but they help spread the product and provide a sensory cue that it is working. Without SLS, many liquid soaps and cleansers would not mix properly or create the rich foam consumers expect.
Is Sodium Lauryl Sulfate Safe to Use?
Yes. Regulatory agencies, including the U.S. Food and Drug Administration (FDA), consider SLS safe for use in cosmetics and personal care products at the concentrations typically found in them. The Cosmetic Ingredient Review (CIR) Expert Panel, an independent scientific body, has also reviewed the safety data and approved its use.
The primary concern with SLS is not toxicity but irritation. For most people, using products with SLS causes no issues. However, for those with sensitive skin, eczema, or certain allergies, SLS can strip the skin of its natural oils, leading to dryness, redness, or itching. This is why many “sensitive skin” brands market themselves as sulfate-free.
Is SLS the Same as SLES?
No, but they are closely related. Sodium laureth sulfate (SLES) is the ethoxylated version of SLS. The chemical process used to create SLES introduces ethylene oxide, which makes it a larger molecule. This larger size makes SLES less penetrating and generally less irritating to the skin than SLS.
A common myth states that SLES is a known carcinogen. This is false. The concern comes from a process called ethoxylation, which can produce a byproduct called 1,4-dioxane. 1,4-dioxane is a potential human carcinogen, but it is not SLES itself. Manufacturers are required to remove this byproduct during production, and the FDA monitors levels to ensure they are within safe limits. The final product is safe, but if you have sensitive skin, switching from SLS to SLES may reduce irritation.
Why Do People Avoid SLS in Shampoo and Toothpaste?
The “no-poo” movement and clean beauty trends have fueled the demand for sulfate-free products. In hair care, the main complaint is that SLS can be too harsh. It can strip color from dyed hair faster and dry out the scalp, leading to flakiness or an overproduction of oil to compensate.
In toothpaste, the concern is different. Some people believe SLS causes or worsens canker sores (aphthous ulcers). Research on this is mixed. Some studies suggest that SLS-free toothpaste may reduce the frequency and duration of canker sores in people who are prone to them, while other studies find no significant difference. If you suffer from recurrent canker sores, trying a toothpaste without SLS is a reasonable, low-risk step, but it is not a guaranteed cure.
What Are the Common Products That Contain SLS?
SLS is everywhere. It is inexpensive to manufacture and highly effective, which is why it is a staple in the cleaning and personal care industries. You will find it in:
- Shampoos and conditioners
- Body washes and bar soaps
- Facial cleansers
- Toothpaste
- Laundry detergents
- Dish soaps
- Household cleaning sprays
- Bubble baths
It is also used in industrial settings as a wetting agent and in some pharmaceutical products as a skin penetration enhancer. Checking the ingredient list on any product is the only way to know for sure if it contains SLS.
Who Should Consider Avoiding SLS?
Most people do not need to avoid SLS. It is effective, safe, and affordable. However, certain groups may benefit from choosing sulfate-free options.
If you have eczema, rosacea, or contact dermatitis, SLS can exacerbate your symptoms. The chemical can disrupt the skin barrier, making it easier for irritants to penetrate and trigger a flare-up. If you have naturally dry or sensitive skin, you may notice that products with SLS leave your skin feeling tight and itchy.
For hair, if you have keratin-treated or chemically straightened hair, SLS will break down those treatments much faster. Similarly, if you have curly or coily hair, which is naturally drier, SLS can strip away the moisture and leave your hair brittle and frizzy.
Are Sulfate-Free Alternatives Effective?
Yes, they are effective, but they work differently. Sulfate-free cleansers use alternative surfactants, such as sodium coco-sulfate, cocamidopropyl betaine, or decyl glucoside. These are derived from plant sources and are generally milder on the skin and hair.
The trade-off is that they produce less foam. Many people interpret a lack of lather as a lack of cleaning power, but this is not true. These gentler surfactants still lift dirt and oil effectively; they just do not create the same rich bubbles. If you are transitioning to a sulfate-free shampoo, you may need to use more product or wash your hair twice to feel the same level of cleanliness, especially if you use heavy styling products.
How to Read Labels for SLS
Reading ingredient labels is straightforward once you know what to look for. SLS can appear under several names, including:
- Sodium lauryl sulfate
- Sodium dodecyl sulfate
- Sulfuric acid monododecyl ester sodium salt
- Monododecyl ester sodium salt sulfuric acid
If you are trying to avoid it, look for products labeled “sulfate-free” or “SLS-free.” However, be aware that “natural” or “organic” labels do not guarantee the absence of SLS. The ingredient list is the only reliable source of truth.
It is also worth noting that SLS is not a preservative. Products without it still require preservatives to prevent bacterial growth, so removing SLS does not automatically make a product “cleaner” or more natural.
What Does the Research Say About SLS and Health Risks?
The scientific consensus is that SLS is not a carcinogen and does not accumulate in the body. The American Cancer Society has not listed SLS as a cancer-causing agent, and no credible human studies link SLS in personal care products to cancer.
The most well-documented side effect is irritation. A 2015 review of the literature confirmed that SLS is a known irritant at high concentrations, but the levels permitted in rinse-off products like shampoo and toothpaste are generally low enough to be safe for the majority of users. The risk increases with longer contact time, which is why leave-on products like lotions and creams are formulated with lower concentrations or different surfactants altogether.
Frequently Asked Questions
Does sodium lauryl sulfate cause cancer?
No. No credible scientific evidence links SLS in personal care products to cancer. The confusion comes from a byproduct called 1,4-dioxane, which is removed during manufacturing.
Is SLS safe for sensitive skin?
It can be irritating for some people. If you have eczema or reactive skin, SLS can strip natural oils and cause redness or itching, so a sulfate-free alternative may be a better choice.
Does SLS in toothpaste cause canker sores?
The evidence is mixed. Some studies suggest SLS-free toothpaste may help people prone to canker sores, while others show no effect. Trying a toothpaste without SLS is safe and may help, but it is not a guaranteed fix.
What is the difference between SLS and SLES?
SLES is a gentler, larger molecule derived from SLS. It is less likely to irritate the skin, which is why many sensitive-skin products use SLES instead of SLS.
