it is type of vasculitis
and very common condition.
let me ans ur questions.
-the best treatment is immunosuppersent like corticosteroid ,methotrexate
antibiotic also given as there is infection in many cases.
may be associated with it if it is due to autoimmune reason .
-change in weather may affect it ,so be careful during it
-no special foods or chemical to take care
-infection surely increase it ,so be healthy to avoid it
it is not a serious condition but u need to be very caution in each thing.