What particle can not penetrate the skin and why could it be considered more dangerous than gamma rays?

Alpha particles cannot penetrate the skin because they are highly ionizing. All energy is lost within a short distance, even in air; any potential energy will have been absorbed by the molecules in the air.

For this reason, Alpha particles have the potential to become very dangerous if ingested or inhaled; all neighbouring molecules, i.e body tissues absorb the photons, risking potential cell damage/mutation.

Alpha Rays cannot penetrate the skin, and could be considered more dangerous than gamma rays because it react with water in the cells Possible cause cell damage.