Asthma Boy is a clinic patient, a young child who is seen by Gregory House in the episode Pilot. He was played by child actor Dylan Basu.
Asthma Boy had already been diagnosed with asthma and had been prescribed a steroid puffer by a previous doctor. He comes to the clinic with persistent breathing problems.
House naturally asks if the boy has been using his puffer regularly. His mother replies he has not because she's concerned about her son using such powerful medication. House admonishes her, telling her the doctor who prescribed the steroids probably had already done the balancing and determined that the side effects of steroids were less risky than the side effects of not breathing, given the importance of oxygen.
However, at that moment, he realizes his primary patient has symptoms that may indicate vasculitis and that, if she does, steroids were the perfect choice. He rushes out of the exam room telling the mother that if she doesn't believe in steroids, she shouldn't believe in doctors either.