In this article, we would like to share the hair thermal damage model conducted by CIRS Testing and Amway (Shanghai), as published in the Journal of Cosmetic Dermatology.

The frequent use of hair dryers can cause thermal damage to the hair. Currently, there are various hair care products aimed at repairing thermal-damaged hair emerged on the market, making it necessary to establish a convenient and stable hair thermal damage model to evaluate the efficacy of such products.

Research Design

Testing Materials: Black healthy hair tresses from Asian people

Establishment of Thermal Damage Model: After wetting the healthy hair tresses, use a hair dryer to blow-dry both the front and back sides. Repeat the wetting and blow-drying process 30 times, which is equivalent to one month of daily hair dryer use.

Using a forced-air drying oven, set the temperatures to 40°C, 60°C, and 90°C, respectively. Place the healthy hair tresses at the aforementioned temperatures for 6 h, 12 h, and 24 h, respectively, to screen and determine the optimal conditions for the hair thermal damage model.

Testing: Observe the Hair Cuticle Morphology under Microscope

• Hair Surface Contact Angle Measurement;
• Hair Moisture Content Measurement;
• Hair Mechanical Properties Testing;
• Hair Protein Leaching Measurement;
• Hair Tryptophan Content Measurement;

Research Results

Establishment of the Thermal Damage Model:

By comparing the cuticle morphology, fracture work, and protein leaching of hair tresses blow-dried 30 times with a hair dryer, the optimal conditions for the hair thermal damage model were determined.

Validation of Effectiveness of the Thermal Damage Model:

Cuticle Morphology:

SEM analysis revealed that healthy hair (A) exhibited intact cuticle scales with smooth edges. Conversely, both the repeatedly blow-dried hair (B) and the thermal-damaged samples (C) showed raised, detached, and fragmented scales, with noticeably roughened edges.

Microscopic observation of the hair longitudinal section provided a clearer view of the cuticle morphology. The cuticle of healthy hair (A) showed no lifting. The repeatedly blow-dried hair (B) and thermal-damaged hair (C) exhibited cuticle lifting, with the lifting observed in heat-damaged hair (C) being more severe.

Hair Surface Contact Angle:

A shift from hydrophobicity to hydrophilicity was observed in damaged hair. Contact angle measurements confirmed that healthy hair and the repeatedly blow-dried hair remained hydrophobic, whereas the heat-damaged hair became hydrophilic.

Hair Moisture Content:

Compared to healthy hair, the moisture content of the repeatedly blow-dried hair showed a highly significant decrease. No significant difference in moisture content was observed between heat-damaged hair and the repeatedly blow-dried hair.

Micro-infrared spectroscopy was employed to analyze the moisture distribution within the hair strands. The redder hues indicate higher moisture content. Healthy hair (A) exhibited relatively high and uniform moisture distribution. A reduction in red areas was observed in both the repeatedly blow-dried hair (B) and thermal-damaged hair (C), indicating decreased moisture levels, which aligns with the findings described above.

Hair Mechanical Properties:

The mechanical strength of hair, as measured by its breaking work, decreases with increasing damage. We observed a highly significant reduction in breaking work in the repeatedly blow-dried hair compared to healthy hair. The breaking work of these blow-dried samples was statistically indistinguishable from that of the thermal-damaged hair.

Hair Protein Dissolution:

Higher protein dissolution indicates more severe hair damage. Compared to healthy hair, the protein dissolution of the repeatedly blow-dried hair showed a highly significant increase. The protein dissolution of heat-damaged hair showed a highly significant increase compared to the repeatedly blow-dried hair.

Hair Tryptophan Content:

Lower tryptophan content indicates more severe hair damage. Compared to healthy hair, the tryptophan content of the repeatedly blow-dried hair showed a highly significant decrease. The tryptophan content of heat-damaged hair showed a highly significant decrease compared to the repeatedly blow-dried hair.

By evaluating the microstructure and physicochemical properties of healthy hair, the repeatedly blow-dried hair, and heat-damaged hair, the validity of the model is demonstrated.

In the field of hair care products efficacy evaluation, CIRS Testing has established six major damage scenario models (covering thermal, chemical, physical, air pollution, UV exposure, and seawater/pool water damage). Through deep integration with three testing dimensions—physical performance, chemical composition and microscopic imaging—CIRS Testing has established comprehensive in vitro efficacy evaluation capabilities.

Our Advantages

Extensive Participants Database: owns a extensive participants database which spans multiple cities across the country, assembling a diverse group of participants with varied consumer needs. This ensures CIRS Testing to meet the broad requirements of different brands in market research, thereby providing comprehensive and authentic consumer feedback for product efficacy evaluation.

Perfect Laboratory Construction: possesses a full set of professional testing equipment, including dermatoscopes, needle-type moisture test probes, ultra-small transepidermal water loss test probes, and scalp sebum meters. By integrating the expert assessments from dermatologists with various technical approaches, we offer extensive efficacy evaluation services for hair care products.

Whole Industry Chain Services: provide one-stop services covering the whole life-cycle of a personal care product, which includes cosmetic ingredient development, physical/chemical tests, toxicological tests (in vivo & in vitro), efficacy studies (in vivo & in vitro), ingredient registration, and product registration.

Our team

CIRS Testing Cosmetic Laboratory has been accredited by the China National Accreditation Service for Conformity Assessment (CNAS) and China Metrology Accreditation (CMA). It is also accredited by the National Medical Products Administration.

With complete equipment and excellent technical competence, CIRS Testing Cosmetic Laboratory received recognition for its testing capabilities both at home and abroad. The Cosmetic Laboratory has created many patents, and has maintained close cooperation and in-depth communication with many national laboratories.

CIRS Testing Cosmetic Team is comprised of a marketing team, customer service team, regulatory compliance team as well as the laboratory, with a total of more than 60 staff. The team keeps on enhancing technical skills and improving its cosmetic service system. It is able to provide a one-stop service to clients, including cosmetic regulations consulting, registration/filing, safety efficacy evaluation, and testing.

If you have any needs or questions, please contact us at cosmetic-ck@cirs-group.com.