Antonia, while this isn't cheap, I strongly advise looking into those battery heated gloves. I grew up in Florida so that frostbite bit holds no water. Bottom line, some of us just have it. I use Serius gloves. They are a bloody fortune but they are a godsend. The batteries are lithium and you can get replacements. As I do adventure travel and am often in the elements, these are what I use. Also I have invested in all manner of handwarmers and damned good down gloves. You can also find battery-heated clothing, socks and goods for people who ride motorcycles in winter. Just as effective for us. I'd stop worrying about the source and deal with the symptoms. Most of what is recommended online is bullshit, and utterly useless. I've dealt with this for fifty years and I've simply bitten the bullet and sprung for high quality top of the line year.