does hair affect heartrate sensor accuracy

After a few runs with the AWS2 I noticed the average bpm heart rate readings are about 3-4 bpm more than my Polar watch average readings over a four mile run. I am referring to the average bpm for the entire 4 mile run. I was wondering if the hair on my arm could be causing the difference. I do wear the AWS2 snugly on my wrist so i know that is not an issue.