Writing on the skin is not the same as tatooing, which is writing underneath the skin. As long as the skin is not punctured, and unless you are using something very unusual such as sulfuric acid to write on your skin, then no, it isn't harmful. It may not look very good, but it does no harm, and will eventually wash off.
It won't hurt you, however... You absorb a ton of stuff through your skin, and ink is no exception. If you write on yourself enough you actually can have liver damage as a result. (Your body breaks down the ink it absorbed, and it breaks it down at the liver/kidneys) Keep in mind, it would take a lot over time to do this.
yes writing on your hands can cause damage because the ink in the pen can go in to your skin and you can get blood poisening.
No, it is not harmful.
No, Carbomer is not harmful to the skin. Carbomer is used to make gels out of liquids, but it doesn't interact with the skin when it's used on the skin.
yes very harmful
yes
no, if anything clay can make your skin softer
yes it can burn and irritate skin...
Yes they are harmful. Sun's ultraviolet radiations are fatal and cause harm to the skin.
yes it is harmful to human it causes skin diseases
Yes, it can injure the skin.
Yes, it can injure the skin.
Yes
UV radiation is harmful to skin. It causes skin cancer.