Shampoos contain some ingredients with the potential for hair loss or health hazards. Manufacturing byproducts become ingredients in shampoo that you will never find on the ingredients list. These byproducts may act as potential carcinogens or neuro depressants, creating toxins in both the liver and kidneys. The actual, listed ingredients almost always include sodium laureth sulfate, a suspected carcinogen that may cause hair loss and/or eye irritation, and similar ingredients. Furthermore, some shampoo ingredients can react to other products chemically, forming other potentially harmful substances.
Carcinogenic Manufacturing Byproducts
Two potentially harmful substances present in shampoos will never show up on the ingredients label: formaldehyde and 1,4-dioxane. As manufacturing byproducts, labeling of them is not required. The Environmental Protection Agency (EPA) shows formaldehyde as a probable human carcinogen.
Dermal exposure happens when you wash your hair. The EPA also reported as early as 1959 that, "Neurological symptoms were reported in the fatal case of a worker exposed to high concentrations of 1,4-dioxine through both inhalation and dermal exposure." 1,4-dioxane depresses the central nervous system. Noncancerous effects of 1,4-dioxine exposure indicated in studies are liver and kidney toxicity in humans and laboratory animals.
Even so, according to the Personal Care Products Council, exposure to these two byproducts found in such low concentrations as are present in shampoo is considered safe. Data is mixed, therefore, on the dangers found in these byproducts.
Sodium Laureth Sulfate
Sodium laureth sulfate (SLES) and its chemically close "relatives" endure constant scrutiny as a possible carcinogen and as a cause for hair loss. Few shampoos have no SLES in them. SLES acts as the detergent and foaming agent in shampoos. A similar ingredient, sodium lauryl sulfate (SLS) can cause eye irritation because of its harshness.
Savyskin.com recommends you avoid all these ingredients in shampoo: sodium lauryl sulfate, ammonium lauryl sulfate, ammonium laureth sulfate, ammonium xylene sulfonate and TEA lauryl sulfate. For users of dandruff shampoos, they recommend avoiding sulfur and selenium sulfide.
DEA and TEA
Diethanolamine (DEA) and triethanolamine (TEA) are used as solvents, emulsifiers and wetting agents in shampoos. According to a 1998 study by the National Toxicology Program (NT), they "found an association between the topical application of diethanolamine (DEA) and certain DEA-related ingredients and cancer in laboratory animals."
Nitrates are used in shampoos to preserve the shampoo formula. When DEA or TEA reacts with the nitrates in the shampoo, a cancer-causing agent forms. A shampoo with bronopol as an ingredient in it may produce this reaction. Therefore, you may wish to avoid shampoos with bronopol.