Which system provides a barrier that keeps hazardous substances from entering the body and essential chemicals and fluids inside our bodies from being lost?

The correct answer is Integumentary system.

The integumentary system includes skin and all its appendages (hair, scales, feathers, hooves, and nails) with the function to protect the body. It protects body from damage, from loss of water, from abrasion from outside and even protects the deeper tissues. On the other hand, integumentary system excretes wastes, regulates temperature, provides synthesis of vitamin D and many other things.