Shear testing usually tests rocks, soil, metals, glass, etc., so you may be wondering how shear testing can improve shampoo. Well, this is more of an indirect method of testing the efficacy of shampoo, but the results help shampoo labs work to improve their ingredients.
Shampoo Does Not Work If Your Hair Is Not Strong
Shear testing is, and can be, used on strands of hair. With a strand of hair placed between two ends of a stretch force testing machine, the hair is measured. Then the machine pulls on both ends of the strand until it breaks. The time it takes to break, plus the amount of length the hair stretched until it broke, is how shampoo manufacturers figure out if a product is effective at strengthening hair and/or making hair healthier.
Employing Test Subjects for the Product and Hair Testing
If you have any question about how well these tests work, or how consistent results are based on whose hair is being tested, you should know that the shampoo companies engage a group of volunteers, usually for pay, to conduct their research. The hair samples are taken at the beginning of the study, examined closely under a microscope, tested for harsh chemicals, drugs, etc., and then put through the stretch shear testing.
Next, the test subjects are instructed to use the shampoo product given and to use it as directed. Within so many weeks, the test subjects come back to supply a hair sample again. They will either continue to use the sample another set of weeks to see if their hair improves, or they will be allowed to quit using the product. If the test shampoo is not producing the expected results, the shampoo company takes this shampoo back to the labs to see what can be done to improve it.
When the Shampoo Is Ready
The new shampoo product is ready when the hair from test subjects can be stretched much longer than the initial shear test. If the hair also stands up to breakage, that is a good sign that the shampoo is ready for market, too. There may be a few other tests for skin irritation and the like, but the hair stretch test results are the ultimate signifier that the shampoo is good to go. Hence, your hair is the item being stretched in the shear testing; first for baseline purposes, and then to test the shampoo's efforts to improve hair.