DEAR DOCTOR K: I had my hair chemically straightened six months ago. I love the way it looks, but I'm worried that hair-straightening products may not be safe. I hear they contain formaldehyde.
DEAR READER: You're right to be concerned. Chemical hair-straightening products pose more of a risk than you may think.
Hair straighteners are also known as hair relaxers, keratin treatments and hair-smoothing products. They work by breaking and reforming the chemical bonds in keratin, which is the main protein that gives shape to each hair.
During the treatment, the hair-straightening product is applied to your hair and left in place for some time. Afterward your hair is blown dry or ironed. One treatment lasts two to three months.
Many hair straighteners contain a chemical called formaldehyde (also known as formalin). This substance is associated with various health problems. The chemical can cause rashes when it comes in contact with your scalp or the skin of your neck and face. The chemical's fumes can get in the air, and breathing in that air can cause irritation of your nose, throat and lungs. The symptoms can include breathing difficulties, heaviness in the chest, sore throat, headache, fatigue, and burning eyes, nose and throat. If you have had many hair-straightening treatments, and never had these symptoms, you are less likely to ever get them.
Formaldehyde can cause cancer in rats. That doesn't mean it also causes cancer in humans, however. The National Cancer Institute and others have conducted studies of workers who are exposed regularly to formaldehyde fumes. Since formaldehyde is used to preserve dead bodies, people who work in funeral homes are exposed to the chemical. Some studies have indicated that rates of certain blood cancers and brain cancers may be higher in funeral workers. It's by no means a proven risk, but there is a reason for people who work with embalming fluid to be concerned.
However, I'm not aware of any studies indicating that hairdressers have a higher risk of cancer. And there's no evidence that people who get their hair straightened every several months have a higher risk of cancer.
There's another concern, too. Hair-straightening products are allowed to contain small concentrations of formaldehyde (0.2 percent). But several hair-straightening solutions have been found to contain well above the allowable limit. For example, one popular hair-straightening product that advertised itself as "formaldehyde-free" actually contained 6.8 percent to 11.8 percent formaldehyde.
If you haven't had rashes and irritation of your respiratory system from past treatments, there is little reason to stop them -- so long as your hairdresser continues to use the same hair-straightening products. As an alternative, ask your hairdresser if he or she has a hair-straightening liquid that does not include formaldehyde; they do exist. Finally, your hair can be straightened without the use of chemicals by using a flat iron. The downside is that this may damage and dry out your hair if not done carefully.
(Dr. Komaroff is a physician and professor at Harvard Medical School. Go to his website to send questions and get additional information: www.AskDoctorK.com.)