I have this problem in the winter, all over and not just the legs. At first, my wife was making home made laundry detergent. Our house was very humid due to the sump pump in the basement (no fan in the bathroom and laundry and bath tub drained into sump pit. There's always water there.) Humidity was what I was thinking. Then I thought about the laundry detergent. It is very pungent. I think it was the Fels-Naptha soap. We switched back to perfume free store bought and I no longer had the problem.
Fast forward to now, I have the problem again. Now I am divorced and can not afford living. I am at my mother's who is very VERY stubborn. Her house is so dry I am getting nose bleeds. My legs are bleeding they are so itchy. It is also freezing in the house with the thermostat set at 68 (I always had mine set at 67 and sometimes would be hot then.) She complains about the cold all the time but won't turn the thermostat up a degree. This is a woman who will drive to 15 different dollar stores looking for spaghetti sauce for $0.79 instead of buying it at the first place for $0.88.
I told her she needs a humidifier. You would have thought I told her she needed to remove her kidneys. She also has so much perfume in the house between air fresheners, candles, and crap she sprays that it is difficult to breathe. She uses the most perfumey laundry soap she can find. I have my own I do my laundry with, which is perfume free but she will strip down my bed to wash sheets when she does hers while I'm at work. As soon as I get into bed, I'm tearing into my legs causing them to bleed because they are so itchy.
Tried to get her not to do any laundry for me, but it would be a waste of water and would break the bank to not put all the sheets in 1 load. Thankfully she had a coupon for laundry detergent and Walgreens had it on sale for $1.99. I spied the perfume free on the top shelf and talked her into it.
So, I agree that the lack of humidity in the winter can be bad with this, but also check the laundry detergent. I don't know if years of using the perfume free detergent made it worse for me, but it started as soon as we started making our own and stopped as soon as I went back to free detergent as well as started immediately again this winter with perfumey detergent.
I'm about ready to move into my car permanently as I don't know how much more I can take, but that's a story for another time.