My Boyfriend Has A Red Line Up His Forearm From

My boyfriend has a red line up his forearm from his wrist to under his arm. It feels warm but not painful. He was doing some heavy digging of a trench for his father. He also has a blister in the palm of his hand that's swollen and red.
Is it possibly an infection? I thought maybe a blood vessel be issue of the strain... But... That's why I'm here asking