Interesting question. As far as I am aware, there isn’t any, other than the general guide of a half inch per month when you average out the phases and occassional hair follicle loss. This is aside from things we should do to stay well: eg eat healthily, exercises, etc – very ill people may loose their hair. Hair is mainly made of the protein keratin, so protein could be a limiting factor if there was none available.
However, we know that our hair growth and density varies among parts of our bodies – and between people. And it also varies depends on our life stage. This is because physiological changes dictate how the hair cells behave. So in principle it could be possible to alter the growth of hair in specific body parts by adjusting the local hormone levels or protein levels. But this is tricky to achieve and hair growth is not well-studied as a result.
Are you trying to get your hair to grow faster? why?
The only way to make your hair grow longer would be to make your hair follicles hold onto the hair for longer.
Each hair grows out of a follicle and as the hair gets longer and heavier, eventually the follicle can’t hold on much longer and it sheds the hair. It’s ok though as it then starts growing another on. How long you can grow your hair depends on you genetics, and in general Asian scan grow their hair longer than Europeans.
All this stuff about feeding your hair amino acids that they talk about in advert is useless I’m afraid. You do need to keep your hair and hair follicles healthy but your hair follicles are nourished by your blood and do not take in stuff from shampoo and you hair is essentially dead. You hair cannot take in nutrients but it does need oil, just like your skin does, to keep to supple and healthy. You scalp provides this through sebum. We wash off the excess and the dirt that gathers (so we smell clean) and this strips the hair of oil (just like your skin) and that is why you need to use conditioner (and moisturiser). The conditions puts a bit of the oil back in the hair to keep it strong, since the hair further from the scalp get’s less help from it you need to condition the ends the most.
The reason for all this is that dry brittle hair breaks and thus you can end up with hair a bit shorter that it could be. The same applies to split ends, you trim them off so they don’t weaken the hair. There is no way to fix split end, ignore the advertising.
In conclusion no, but ignore the shampoo ads coz they’re nonsense and remember to condition!