What is the best defense against most viral diseases?hygiene,immune system or just simply your skin

The best defense against viral or bacterial disease is all the above. Intact skin, the epidermis is the first line of defense. It creates a barrier against infection. You also have normal flora on your skin that fights pathogens.

Good hygiene is also important in the fight against disease. We are bombarded by pathogens daily, good hygiene will keep them at bay.

A healthy, functioning immune system is also paramount in the fight against disease. Most of us don't get ill because of our immune systems. Compare this to someone who is immunocompromised, they get ill frequently and stay sick longer. If immunocompromise is severe, they can not fight off pathogenic organisms and perish from opportunistic infections.