...let me be more specific...
YOUR hair.
The journey to understanding what to do and how best to grow healthy hair begins with finding out some basics like:
Hair type: fine, course
Hair density: thin, thick
Hair porosity: high or low
Let's run through each of them and then you can do the test at home to figure out where your journey starts.
Hair Type:
This is pretty straight forward to determine. If you look at a strand of hair, how thick does it look? Do you think it's thin and easily breakable or thicker and you can feel it more between your finger and thumb?
Hair Density:
How easy is it for you to grab all your hair with one hand? The thicker your hair is the more difficult it is (do not confuse this with the curl type. If you, for example, have tighter curls, your hair might spring back and resist being put together so tightly). Thin density hair is very common in Scandinavian countries.
Hair Porosity:
Hair porosity describes how well your hair absorbs and retains moisture, divided into three categories:
Low porosity: Cuticles are tightly packed, making it hard for moisture to penetrate but also making hair less prone to frizz. Products may sit on top of the hair rather than absorb which could make the hair look greasy.
Medium (normal) porosity: Moisture is easily absorbed and retained, and hair typically responds well to most products. We all want this as it's the easier type to manage with products.
High porosity: Cuticles are raised, often due to damage (heat, bleach etc) or genetics, making it easy for hair to absorb moisture but also lose it quickly. Hair may become frizzy, dry, and prone to breakage. Many people with high porosity hair describe it as being "thirsty" because it loves product.