If you use regular soap on your face it's because the soap water has a high pH whereas your skin has a slightly acidic pH of around 5.5. So the soap disrupts the acidic barrier of your skin which prompts the skin to produce more sebum (acidic) to restore said barrier. [this is a simplification]
This happens on all your skin but it's more egregious on the face because the skin is more delicate there.
This happens on all your skin but it's more egregious on the face because the skin is more delicate there.
No idea for the shampoo though.