What are the human body’s natural barriers to diseases and other sicknesses?
Joni D
Please let me know asap, because this is due soon for health class and (I can’t believe it), but there is not much info online. PLEASE HELP ME!! 
I have skin, immune system, but is secretions of stomach and membranes one??
The skin, mucos membranes, and our immune system.
Maybe try looking up the immune system and how it works – you could elaborate on that further and explain how immunisation works by ‘kick-starting’ the immune system and familiarising it against new strains of disease.
Skin is one, plus the immune system, and your health book should give you the other answers.
You might start with the work of Weston Price, DDS.
Most notably, his book Nutrition and Physicall degeneration, also Root Canal Cover-Up by George E. Meinig. They are pretty easy to find and have some great discoveries in them about how the body deals with infection. All I can think of at the moment.
Tears, saliva, skin, sweat, vaginal secretions, ciliated membranes and the ones you mentioned are all natural barriers to disease. Even ear wax, leukocytes, vitamin A and C are considered natural defenses of our body if you want to go that far. I hope this helps.