The best water temperature for shampoo is about 40 ℃. If the water is too hot, it will damage the hair and increase the risk of hair loss. If the water is too cold, it is easy to cause poor blood flow, so it is best to wash your hair with water that is neither too cold nor too hot. 

The reason why people wash their hair with the best water temperature is that warm water can expand skin capillaries and superficial dermal blood vessels, open sweat pores and promote metabolism, making warm water easier to decontaminate than cold water, especially the dirt attached to the scalp, which is easier to be removed. If it is in cold winter, washing your hair with cold water will cause colds, headaches, and even poor blood flow, resulting in increased blood pressure in patients with hypertension; Even in hot summer, the temperature difference in the head will be large, resulting in diseases such as fever and cold. In summer, many people wash their hair with cold water, but they unknowingly have a headache. This is because the arteries and blood vessels in the head and brain are very fragile. After exercise in the hot season, the head often sweats and blood vessels dilate. At this time, if washed with cold water, it may lead to abnormal intracranial blood vessel function, dizziness, vomiting and so on, It may even lead to intracranial hemorrhage, so you must wash it with warm water after a lot of exercise. The elderly with cardiovascular and cerebrovascular diseases should be more careful! Washing hair with cold water will also make the sebum hard to dissolve, making the dirt on the scalp difficult to wash off; Cold water shampoo can also lead to rapid contraction of scalp blood vessels, making hair dry and fall off and premature aging. Although it is very comfortable to wash your hair with water with too high water temperature, too high water temperature will lead to the thinning of the lipid membrane layer required by the scalp. At the same time, it will also make the hair lose its softness due to heat, make the hair root very brittle, and even cause serious hair loss. In short, you can't wash your hair with too cold and too high water. It is recommended to wash your hair with water at about 40 degrees Celsius!