Some of you may have caught this one on BGLH, but here it is if you haven't. This is to answer the question that many of you ask me.......is it possible to damage hair while stretching it to combat shrinkage and tangling?
The Short Answer
Yes stretching hair excessively could be harmful but low levels of stretching are perfectly fine and can be useful in hair maintenance.
1. Hair recovers very well from low level stretching with the help of water
Scientists have demonstrated that hair can recover very well from a 20-30% extension of the strand (Journal of the Society of Cosmetic Chemists, pp 13-26, 1996). The stretched strand will recover its full strength once the stretching force is released and the hair is dipped in water. Why the dip in water? Water has a key role in making hair flexible and strong as it slightly changes the protein (keratin) in hair. Do note that for styling, you do not have to do the dip, it may reverse the stretching process. However, when you are done with the style, a little water will help you have stronger hair to handle the next styling or maintenance process.
2 How can you tell if you are in the safe limit of stretching?
It is pretty easy to read a 20-30% stretch in a lab but not really possible in a real life situation. As a general guide, if you retain some texture in your hair while stretching, you are probably in the safe region. Aiming to completely smooth out a curl or kink with stretching has the potential to over-stretch the hair. As a general rule if your hair shrinks to 4 inches and is actually 10 inches in length, attempting to stretch it to 6-8 inches is probably better than trying to get to the full length.
3. What happens if you stretch hair over the safe limit?
By now, most of us will know hair has a cortex and a cuticle. The cortex is the strength bearing part of hair and it will generally not suffer too much. However, the cuticle of hair can undergo a dramatic fail with whole scales lifting and separating from the cortex. This can progress to sections of the hair having no cuticle and therefore the cortex in these parts gets exposed to the full brunt of damage that the cuticle would normally protect it from.
4. Should you stretch hair when it is wet or dry?
You should avoid stretching hair when wet, it can easily break (Journal of the Society of Cosmetic Chemists, pp 449-467,1978). However, when it is completely dry, it lacks flexibility. Stretching hair which is around 70-80% dry is likely to be a good mix of flexibility and strength.