Hair Thickness Changes by Seasons

I had really thick hair up until I was 16 years old. Since then it is about 1/3 the thickness. I have tried vitamins and have tried to eat alot of protein etc to help. I am 52 (female) and after all these years I cannot help but notice a pattern. During the winter months after December my hair will have regrowth with new hair and actually thicken to the point that my scalp is not visible. Is is possible that cold and sinus medicines such as sudafed, cough syrups, and antibiotics [non penicilin] have ingredients that would contribute to hair growth? As soon as the weather heats up in the summer my hair starts falling out again by the brush full. What do you think? Thank you for your time and consideration.

What you say is logical, it is just not what we normally see in humans. Why humans have developed asynchronous hair growth, why we do not grow and shed hair all at once and the evolution of this is not known. What you are suggesting is that in you there is some seasonal variation in your hair density and that shedding may occur as the seasons get warmer, I do not doubt your observations, but I do not have a basis for understanding it. I am convinced that in the summer when we sweat a great deal and get our hair wet from sweat, we may actually produce more friction when we brush or comb the hair. That might account for the hair that comes out when you brush your hair in the summer. Also, some people wash their hair more frequently in the summer when they are out and about because they get it ‘dirty’ more easily. That might explain what you are observing. Clearly, there is a suggestion that there is some middle ground in your history and that some climate problems do occur in the summer in your situation. Do you live in a warm/hot climate?