Will being in the sun too long without Sun screen cause skin cancer?

Cumulative sun exposure causes mainly basal cell and squamous cell skin cancer, while episodes of severe sunburns, usually before age 18, can raise the risk of developing melanoma. Other less common causes are repeated X-ray exposure and occupational exposure to certain chemicals.

nasa 3

this null effect is caused by a weak manipulation and ineffective internal validity. in a scientific study, as the one dr. morimoto is trying to perfom, internal validity refers to the confidence placed in the cause-effect relationship and to how well an experiment is done and able to eliminate confounding variables.