There are many spelling rules in English. Here is one.
2) Prefixes
Rule 1: The spelling of a word never changes when adding a prefix, even if the first letter of a word is the same as the last letter of a prefix. (Don’t have to hyphenate prefixes)
Note: You do not have to hyphenate prefixes
Example: co-operate/ cooperate, un-natural/ unnatural
Exceptions: There is none for this rule