Science of hair frizz: Kao pinpoints UV rays as culprit behind untamed tresses

31 Jan 2023 --- Japanese scientists have discovered that ultraviolet (UV) rays are closely related to frizzy hair that occurs on the outer layer of the head, which disrupts the alignment of hair bundles and causes uneven appearance. 

“Uneven frizzy shape of every single hair fiber is considered to be due to the innate and/or acquired accumulation of damage caused by hair dying, heat setting and the like. This has been difficult to fully be resolved by daily hair care,” state the researchers.

The study was conducted by the Analytical Science Research Laboratories and Hair Care Products Research Laboratories of Kao Corporation. Based on these findings, Kao plans to proceed with the development of products for UV-protection that can be readily applied to hair in the future.

Hair is “cleaved” by UV rays
Upon closer investigation of the mechanism of how the frizz occurs, it was found that disulfide bonds inside the hair are “cleaved” by UV rays, which leads to some of them “significantly undergoing reformation in a distorted manner,” which is similar to the mechanism of hair perms.

When comparing the outer and bottom layers of hair, Kao researchers found that there are “almost straight hairs with minimal frizz” beneath the outer layer of hair. Meanwhile, “significantly more frizzy hairs” were observed on the outer layer of the head, which greatly affects the appearance of the whole head of hair.

Based on these observations, the study attempted to identify the causes and mechanisms of the frizzy hair that specifically occurs on the outer layer of the head.

“In everyday life, some factors of influences are accumulated in the hair located on the outer layer of the head. One is exposure to sunlight outdoors in the daytime. Another is the distortion of hair shape, which is frequently seen due to contact with pillows over nighttime, for instance,” detail the researchers.

Upon closer investigation of the mechanism of hair frizz, it was found that disulfide bonds inside the hair are “cleaved” by UV rays.As a result of evaluating these two factors, the Kao team found no significant changes of hair shape related to exposure to sunlight alone. However, when the hair was held in a distorted state after the sunlight exposure, the degree of frizz significantly rose.

Furthermore, the longer the hair was held in the distorted state, the frizz level gradually increased over time. On the other hand, when UV rays were filtered out of the sunlight, the change of frizz level was suppressed, indicating that UV rays and distortion are the major factors in the occurrence of frizz.

Mechanisms of frizz
The numerous disulfide bonds that are present in hair proteins work as cross-links of the proteins “like a ladder,” the Kao researchers explain.

Although these disulfide bonds have been reported to be cleaved by UV rays, the causal relationship between the breakage of the bonds and the occurrence of frizz remains unclear. 

In this study, the changes in the amount of disulfide bonds were measured over time during the process of frizz occurrence by using Raman spectroscopy.

“The time-course analysis revealed that during exposure to sunlight, the disulfide bonds are cleaved and decreased due to the effects of UV rays, after which they increase [reforming once again],” the researchers explain.

These results suggest that some of the broken disulfide bonds have a tendency to be reformed over time, first at a rapid pace and then more slowly as time progresses. However, when the hair is in a distorted shape – such as in the case of “bed head” – exposure to UV rays can lead to the broken bonds reforming in a deformed manner.

“The frizz is directly related to the gradual reformation process of disulfide bonds between the proteins in a distorted conformation,” conclude the researchers.

Even prior to this latest Kao study, it has been known that excessive sun exposure is the most frequent cause of hair shaft’s structural impairment.Shielding hair from the sun
Even prior to this latest Kao study, it has been known that excessive sun exposure is the most frequent cause of hair shaft’s structural impairment. 

Previous research has evidenced that photochemical impairment of the hair includes degradation of hair pigment, in addition to the loss of hair proteins. In particular, UVB radiation is responsible for hair protein loss and UVA radiation is responsible for color changes.

Meanwhile, the absorption of radiation in photosensitive amino acids of the hair – and their subsequent photochemical degradation – is known to produce free radicals. This has an adverse impact on hair proteins, especially keratin. 

Melanin can partially immobilize free radicals and block their entrance in the keratin matrix. It also absorbs and filters adverse UV radiations. Therefore, melanin is important for direct and indirect protection of hair proteins. 

Protecting the cuticle is very important for keeping the hair shaft’s strength. One can achieve that by avoiding noxious impacts or by implementation of hair care products with UV filters. Nowadays major studies are conducted in order to create hair care products that prevent hair damage.

Red algae, in particular, has been proven to “easily process” UV rays acting on hair, as well as pollution, in its delivery of antioxidant protection.

By Benjamin Ferrer