Shampoo surfactants can cause hair damage and low strand density

28 Nov 2023 --- Korean scientists warn washing hair with surfactants can cause structural damage while decreasing its internal density. They believe cuticle-sealing formulations may effectively inhibit this phenomenon. 

“Generally, thicker hairs contain more than one loosely packed porous region, called the medulla, located near the center of the hair. These multiple porous regions appear spherical and hollow inside a series of vacuoles along the fiber axis” explain the researchers, writing in Cosmetics.

Healthy hair solutions
The scientists note that the more severe the degree of cuticle lifting, the more the internal density of the hair is reduced by surfactants.

“In addition, the study confirmed that a decrease in internal density could be prevented by sealing the cell membrane complex, and it was suggested that this reduced internal density may reflect the pore structure of hair.”

Surfactants remove essential lipids like squalene and esters from hair during washing.This phenomenon was revealed based on optical analyses such as optical microscopy, scanning electron microscopy, drop shape analysis, atomic force microscopy and single hair analysis.

“When the experiment was conducted using only water without a surfactant, black areas [pores in the hair, indicating loss of density] were not generated,” say the scientists. “However, the number of black areas was reduced. Therefore, the black areas were caused by surfactants.”

Treatment with low-molecular-weight materials was shown to replenish the internal density of the hair.

Structural integrity of hair
Hair fibers, as explained by the study, encompass a meticulously structured arrangement, comprising a dehydrated cuticle, a cortex and occasionally a medulla. The cuticle serves as a protective shield, encompassing the cortex. It comprises multiple layers, typically six to eight.

The cortex, which houses cells and cell membrane complexes, plays an important role in maintaining the hair’s structural strength. Notably, thicker hairs often feature porous regions — referred to as the medulla — situated near the hair’s center. 

This porous medulla has a positive correlation with hair diameter and is more prevalent in certain ethnic hair types and beard hair compared to others.

Surfactants commonly found in hair care products emerge as catalysts for cuticle lifting, a phenomenon where the cuticles detach and disrupt the hair’s structural integrity. 

This lifting, which occurs when a hydrophobic surfactant layer forms on the hair, ultimately leads to the failure of the cell membrane complex, worsening structural damage.

Using imaging techniques, the scientists looked at defects in the medulla indicating the presence of internal pores. These pores, enlarged by oxidative damage, heat or surfactant exposure, undergo an increase in volume and size as the damage intensifies. 

Surfactants, known to cause lipid loss in hair and protein depletion, were discovered to play a crucial role in the formation of these internal pores, challenging prior beliefs that pore occurrence was solely linked to oxidative damage or heat exposure.

Hair lipids under attack
Surfactants remove essential lipids from hair during washing. “Surfactants penetrate directly into hair and remove more hydrophobic lipids, such as squalene and esters,” specify the authors.

“Although the route by which surfactants penetrate hair is unknown, the cell membrane complex may be the most likely candidate because it has a noncovalent structure rather than a covalent lipid structure,” they note.

“When lipids in the hair are lost and hydrogen bonds within the hair are broken, the internal structure of the hair is disturbed.”

Pores, which are represented by a region of low internal density, formed immediately after washing up to four times. However, no pores were formed after four washes. 

“This indicated that the bonding strength in the area where the pores were created was weak. The region of low internal density created this way was easily filled with other amino acids,” detail the scientists. 

The scientists note that the more severe the degree of cuticle lifting, the more the internal density of the hair is reduced by surfactants.The report suggests the portion of hair density lost by the surfactant can be replenished with lipid components supplied by the sebaceous glands of the scalp or with external nutrients supplied during shampooing. 

“To prevent the loss of internal components through the cell membrane complex, we attempted to seal the cuticle, which was found to prevent the loss of pores more effectively than the other surface treatments,” comment the authors.

“This implies that the ingredients inside the hair leak out through the cell membrane complex, and cuticle-sealing technology is important for hair damage repair. In the future, additional research will need to be conducted to identify the components released from inside hair.”

Prioritize cuticle care
Protecting the cuticle is very important for keeping the hair shaft’s strength. This can be achieved by avoiding noxious impacts or by using hair care products with UV filters. 

Earlier this year, Japanese scientists discovered that 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.

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. The marine ingredient is being leveraged by custom beauty company Prose, in partnership with climate tech company BreezoMeter, in the creation of personalized hair care NPD.

By Benjamin Ferrer