Shampoos and conditioners are marketed as being formulated to keep hair healthy, shiny and free of dandruff and tangles. Despite this, many shampoos on the market contain ingredients that may actually damage hair and irritate the scalp. In extreme cases, some of these ingredients may even cause or exacerbate hair loss. These additives can be avoided by taking the time to read the labels on hair care products.
Sodium lauryl sulfate (SLS) and ammonium lauryl sulfate (ALS) are surfactants found in many inexpensive shampoos because they produce a large amount of foam. According to Healthy-Communications.com and the Journal of the American College of Toxicology, these sulfates were found to be irritants in patch tests at concentrations of 2 percent and greater, which is a much lower concentration than the 20 percent found in many shampoos. Additionally, rat studies have shown both SLS and ALS cause damage to hair follicles, potentially resulting in hair loss. Sodium and ammonium laureth sulfate, which are closely related to the aforementioned ingredients, were found to have irritant effects as well.
Sodium chloride, better known as table salt, is used as a thickener in shampoos and conditioners containing sodium lauryl sulfate. It's a contributing factor to the eye irritation experienced with most shampoos, and it may also cause dry and itchy scalp. It may also cause hair loss. In shampoos containing ammonium-based surfactants, ammonium chloride is used instead.
Formaldehyde is used in some shampoos and conditioners, including some baby shampoos, as a preservative because of its low cost and disinfectant qualities. Formaldehyde may cause damage to DNA, and excessive exposure to formaldehyde may cause some hair loss.