The study was conducted by Kao Corporation’s Analytical Science Research Laboratories and Hair Care Products Research Laboratories from mid-2021 to late 2022.
Hair on the outer layer of the head is typically affected by two factors — exposure to UV rays and distortion of hair shape. The latter is often due to the interaction between the hair and pillow during sleep.
Taking into account both factors, artificial sunlight was adjusted to match the intensity of UV rays in summer and irradiated on a hair sample for four hours.
The hair was then left in a distorted state by applying a constant force over a specified duration.
Changes in the disulfide (S-S) bonds — cross-links of hair proteins responsible for tensile strength of hair and its susceptibility to damage — were measured throughout the process.
It was found that when the hair was held in a distorted state after UV exposure, the degree of frizz significantly increased. In fact, the longer the hair was held in that state, the higher the frizz level rose.
Furthermore, when UV rays were filtered out of sunlight, the changes in frizz level quelled.
“The findings suggested that when hair was exposed to UV rays and left in a distorted state over time, some of the cleaved S-S bonds would reform in a contorted manner, which leads to the occurrence of frizz. This mechanism of action is similar to that of hair perms.
“Also, the impact on the outer layer of the head is significantly larger than on the inner side, resulting in an uneven hair shape,” said Toshihiro Tamura, R&D Core Technology, Analytical Science Researcher at Kao.
Protect the crowning glory
According to Tamura, hair that is light-coloured, thin, and chemically treated is more sensitive to UV rays, and tends to get frizzy easily.
The accumulation of damage from UV exposure and chemical treatments, such as perming and hair-colouring, commonly leads to a frizzy and ragged appearance of the hair.
“It is very difficult to completely restore UV-damaged hair to their original condition by using regular hair care products. Therefore, UV protection for hair is very important,” he added.
Based on the study findings, Kao has recognised a gap in its portfolio and is working to develop UV-protection products that can be readily applied on the hair.
“Currently, our line-up does not include UV-protection products dedicated to the hair, although some sunscreens, such as Biore UV Athlizm Skin Protect Spray and Biore UV Aqua Rich Aqua Protect Mist, can be applied not only on the face and body, but also on the hair. We also have several brands with product lines that tackle frizzy hair, including Essential Flat and John Frieda,” Tamura said.