Natural Radiation on Mars is much higher compared with Earth. The thin atmosphere provides only a small shielding effect against harmful solar radiation and cosmic radiation. Mars also lacks the magnetosphere that protects Earth.
Exposure to dangerous levels of radiation causes cancer. Any exposure to radiation, no matter how slight, poses some risk. Small dose - small risk of cancer. High dose - high risk of cancer.
Nevertheless, there are defined legal limits for exposure during work for several professional activities, such as for X-ray assistants, airplane personnel, etc.
Houses should be equipped with a shielding, thick enough to reduce the radiation to a level equal to Earth, that is, almost zero. Best protection may be achived with houses built in natural caves or set into cliffs or hillsides.
Space suits must be designed with radiation in mind. The suit should provide adequate shielding for the occupant. It may be necissary to design suits with several grades of protection. Suits designed for short-term use can carry lighter shielding which would reduce weight and improve manuverability.