Smoking is definitely harmful for asthma. Any kind of smoke whether if it be cigarette smoke or smoke from a fire can trigger an asthma exacerbation. So you can imagine anyone who has chronic airway inflammation from their asthma to begin with, who smokes cigarettes on a daily basis they're just going to make their situation that much worse.
Often times I see patients who continue to smoke with their asthma, and it doesn't matter what medicines I give them, I won't be able to get their asthma under control until they stop smoking. Another reason to be concerned about smoking with asthma is there's thought to be a link between asthma and COPD which stands for Chronic Abstractive Pulmonary Disease.
It is thought that patients who have underlying asthma who continue to smoke, may go on to develop COPD later in life. This means they'll have higher risks of emphysema and possibly lung cancer.