I have a tough head and chest cold...Should I skip my aerobic exercise?

Probably. If you have chest congestion, a cough, or a fever, you are probably best avoiding strenuous physical or aerobic activity. This can aggravate your already compromised lungs and worsen your problem.
Skip if chest cold. We often use the "neck rule, " meaning if all symptoms are above the neck (only a scratchy throat, runny nose, congestion), and there is no fever or major fatigue, then light aerobic activity is permissable and may boost the immune system. However, if there is a chest cough, shortness of breath, fever or major fatigue, then wait until these symptoms resolve before returning to exercise.