However, it's important to note that:
* Matt Smith as a person does swear. This is normal for most actors. It's just that he doesn't do it in his role as the Doctor.
* Other characters in Doctor Who have used mild swearing. Some companions or other characters have used words like "damn" or "bloody," though these are infrequent.
* Doctor Who has evolved over the years. Earlier Doctors were known to use stronger language, but the show has become more family-friendly over time.
So, while Matt Smith doesn't swear as the Doctor, he might in other roles and in his personal life.