A low-dose radiation exposure harmful I think that any exposure to any type of chemical can be harmful just because we are all made up different and our bodies all process food water etc ... differently. So yes if you are exposed to a chemical you may have a good chance of it harming you.
Radiation is harmful. Small doses less so than large ones. However, radiation exposure is cumulative. This means that the radiation from 10 small doses accumulates in the body to make a larger dose. The body can cleanse itself from some of the effects, but not all. Because of this low-dose radiation exposure is harmful.
Low dose radiation exposure is harmful, it does come with side effects and the more times you are exposed to it, the more likely these side effects are to show. However, it is not in the same ball field as being exposed to regular doses of radiation and it has been controlled in a way that it is quite safe to use on occasion, but that doesn't make it risk free.
Low-dose radiation is not harmful since we are surrounded by it constantly; from the sunlight, to our cell phones, to an hour long plane ride. The exposure to radiation received while riding in a commercial jet liner is much higher than what we receive on the ground, yet there is no evidence that business workers making hundreds of flights a year are at any more radiation-related health risks.