This is a difficult question to answer without knowing a bit more about why your doctor
took the hair sample.
In general office practice, the most common reason to take a hair sample is to evaluate for the cause of unexplained hair loss. For example, by looking under a microscope at the ends of the hairs, a dermatologist
might be able to tell whether the hair loss is caused by telogen effluvium, which is a specific type of hair loss caused by a major stress on the body. Similarly, your doctor can detect certain types of fungal infections of the hair, if there is a concern for that as a cause of hair loss.
Other uses for hair analysis include testing for the buildup of heavy metals and other toxins from the environment. Although this is used often in forensics and research, the results are difficult to interpret and it is not standard practice to make medical decisions on the basis of these results.
The final common use of hair analysis is to look for the presence of illegal drugs, which can collect in hair shafts and stay there many months after they have already washed out of the blood and urine.
Talk to your primary care doctor
if you have more questions.