If you have been a straight-haired natural for years or months, then there is a strong likelihood that your hair is damaged. Regardless of if you call it heat damage or heat training, they both refer to the same outcome. This is what chemist JC from The Natural Haven has to say:
“High heat makes physical and irreversible changes to your hair at a molecular level. High or prolonged heat can physically and irreversibly change the natural structure of protein. Hair is made up of a protein called keratin. Keratin in hair has a natural twist in it called an alpha helix. This twist is present in all hair straight or curly. If you heat keratin to around 215-235°C (419-455F) the alpha helix starts to melt. This is a physical change and it is irreversible, your hair will retain the shape of the melted keratin at a molecular level. Your hair shows you this molecular damage by not getting back into its natural curl or wave and staying straighter.”
Please note that heat damage manifest itself in different ways: loosened curl, loss of curl, excessive dryness, and excessive frizz. Do not think that because your hair is not bone straight that it must not be damaged. To reduce the risk of heat damage, try limiting direct heat (i.e. flat iron, blow-dryer, or curling wand) to a few times a year and remember to use a heat protectant with every use."
Using permanent hair dye strips the hair of its natural moisture, loosening the elasticity and making it more vulnerable to breakage. This is what author Audrey Sivasothy of The Science of Black Hair has to say:
“Whenever you alter or manipulate the hair’s protein bonding arrangement a slight relaxing effect can occur. These curl pattern changes are less likely to occur in coarse hair textures (coarse refers to the diameter of the hair fiber, not the feel of the fiber), and are more likely to occur in those with fine to medium hair textures. Prior damage may also influence whether or not you experience changes in your curl pattern. Using a protein reconstructor after coloring may help some lost curls find their way again.”
Since hair is dead it only accumulates damage without recovery. Regardless of if your hair is virgin, color treated, or relaxed, all hair only gets progressively damaged over time. Therefore, it is important to have a protein-moisture balance. If you are washing your hair daily, then you might be experiencing hygral fatigue. Charlene Walton says, "Hygral fatigue is the result of constant, excessive swelling of the hair cuticle as water is absorbed and the contracting of the hair cuticle as it dries.” Like any other over manipulation, this stress can cause the hair to become weak and susceptible to breakage. Making sure you a not saturating your hair with water everyday and maintaining a healthy balance of moisture and protein can prevent this from happening.
Read more: Does Natural Hair Need Proteins?
Transitioning is the best recovery. If deep conditioning and protein treatment will not revive your curl, then you can either cut the damage at the line of demarcation or transition while cutting a little hair over time. Remember, damaged hair is more susceptible to breakage, so excessively dry and tapered ends can make it challenging to wash and style your hair. It’s up to you to decide if maintaining unhealthy length is worth compromising healthy length.