The length of dyeing time is directly related to dyeing speed. If the dyeing time is long and the temperature is high, the color will be darker. At the same time, hair cream also does some harm to the scalp. The reason why the hair roots are not dyed first is to reduce the contact time between the scalp and the hair dye and reduce the damage of hair dyeing to the scalp.
Extended information: types of harm to human body caused by hair dyeing;
1. Oxidants are quite destructive to hair keratin and are easy to cause damage to hair. Regular use will make hair dull, fragile, split and easy to fall off.
2. Most permanent hair dyes use aniline dye intermediates, which are highly irritating and toxic in cosmetic raw materials. Some people will have allergies when dyeing their hair, even dizziness, nausea and other symptoms.
3. Hair dye consists of two components. When in use, mix them evenly and then apply them to the hair. At the moment of mixing, a chemical reaction will occur, producing a high concentration of harmful gas-dioxins. Dioxopharynx is a strong carcinogen recognized by WHO. It enters the human body through the respiratory tract and interferes with human endocrine. Both estrogen and thyroid hormone are disturbed. Long-term exposure will lead to genetic variation and abnormality, and induce diseases such as cancer.
reference data
Hair Dyeing-Baidu Encyclopedia