What would be causing getting shocked when touching my car door? on 2003 Pontiac Grand Prix

I have been getting multiple static shocks when opening my car door, closing it and putting in gas. I have had my ground wire checked and cleaned. What else would be causing this issue?

Asked by for the 2003 Pontiac Grand Prix
"Static electricity," look it up! Hint, type of clothing and cold dry air can enhance it so check it out. Nothing wrong with the car! Doesn't happen much at all in the summer time. Humidity and different clothes, even your shoes!!