What is a Half-Head Test?
A half-head product test is a method of applying hair product on your hair that gives you the most accurate information about the usefulness and result of the product. Half-head testing is the standard procedure among cosmetic scientists.
Every Hair Blogger Should Do Half-Head Tests
But very few bloggers actually do, and their readers end up paying the price. The thing is, without proper comparisons, it’s practically impossible to tell what a product is doing to your hair, or how it compares to a product you’ve used before. Thus, what ends up happening is bloggers end up marketing not the success of the product, but the success of their current hair-styling attempt.
In the sections below, I describe the details of the why and how of half-head tests.
Doing a half-head test is super easy
Simply part your hair down the middle, putting your product of choice on one half, and keeping the other half product-free so that you can tell what difference the product is creating.
Doing a half-head test gives you accurate results
When you review a product on your entire head, there are many variables that are impossible to control perfectly in an at-home setting. Here are some of them:
You use slightly different amounts of shampoo/cleanser each time. This is pretty obvious: if your hair is more or less greasy at the start of your product review, the product will behave differently. Even if you were to be a stickler and measure out an exact amount of shampoo each time, you still have other variables to worry about like the temperature of the water (which will affect how well the shampoo cleans), and the amount of time that you spend sudsing and rinsing.
You use slightly different amounts of conditioner. When you’re reviewing a styling product or a leave in, the amount of rinse out conditioner you used in the shower makes a difference for how your test product behaves.
You used a different conditioner than other times. Don’t overlook product combinations, they are a powerful thing. Conditioner “A” may affect your test product differently than conditioner “B.” And unless you have those two photo side by side, you can’t tell whether it’s your test product, or the combination that is giving you results. Same goes for shampoo by the way.
You kept your hair in a towel for shorter or longer than other times. Does this one even need an explanation? We’ve all seen that drying too much before applying product can lead to frizz.
You showered for a longer or shorter amount of time. Just like the towel variable, this one affects how much water got absorbed into your hair, which means it will affect how long it takes your hair to dry, which will affect the product performance
Your shower water was a different temperature. This can also affect how much water your hair absorbs, although to a lesser degree.
You styled your hair slightly differently. Whether its time spend styling, or technique, you probably varied it from wash to wash, which can affect how much definition you get in spite of the product that you used.
All of those factors combined mean that it’s really hard to distinguish which observations are thanks to the product, and which of them are due to the above inconsistencies. That’s why half-head tests are great. They eliminate a majority of those variables and allow you to get a much more accurate idea of how a product works.