Do Cornrows cause hair loss or push back your hair line?

I`m a 15 guy with pretty straight hair but I keep my hair long and I like to have cornrows since they are low maintenence and look pretty good on me... but when I take out my cornrows after 2-3 weeks to give my hair a thorough washing, I have clumps of hair coming out in the shower. My cousin (shes the one who braids my hair) tells me that since my hair is in cornrows that all the hair that I naturally lose everyday stays on my head and then all the hair from those 2-3 weeks falls out at the same time when I take out my braids. But I`m looking for some advice from some other people. Someone tell me if I should stop getting cornrows or is my worrying unnecessary. [For anyone who doesn`t know "braids" and "cornrows" were use interchangeably in this post]