Most prefixes don't take hyphens when joined with a word. There are exceptions, but, if you always take out the hyphen, you'll be right many more times than you'll be wrong.
If you want to know a tad more about the exceptions, then leave in the hyphen when two Is (anti-inflammatory for example) or two As (intra-arterial) come together. This is generally correct all the time. 16CMS* 7.85. However, when two Es fall together, look up each such conjoined word in Web11**. This combo seems to have many more exceptions, such as these dictionary entries: preemergence yet pre-engineered.
Also anytime a prefix or suffix is added to a proper noun, a hyphen (or sometimes an N-dash) is needed.
Back to prefixes in general.
In Web11, you'll find these prefixes listed with a hyphen following each entry: anti-, bi-, mid-, pre-, etc., but THE HYPHEN IS JUST TO HIGHLIGHT ITS PREFIX CAPABILITY. DO NOT USE THE HYPHEN WHEN JOINING WORDS TO THESE PREFIXES in general. Just like when looking up other words within Web11, you'll find "distinguisher" elements depending on how the word is used: adverb, adjective, preposition, etc. So the prefix form may be designated by the hyphen after (or the hyphen before when speaking of suffixes), but that is all it is. An identifier. Remember "less" is a word in and of itself, and yet "-less" is the suffix form. Again the hyphen (before or after) is just to highlight how this particular prefix/suffix entry is available for joining with other words. WITHOUT THE HYPHEN. Here are four examples taken directly from Web11: childless, witless, dauntless, fadeless.
Can you tell this is a particular pet peeve of mine? Ha! We all have them. This is one of mine. But it also makes me a great copy editor.
And I share this knowledge to help make your manuscripts shine with a professional polish. Best wishes and many successes to us all.
*CMS = The Chicago Manual of Style, Sixteenth Edition
**Web11 = Merriam-Webster's Collegiate Dictionary, Eleventh Edition
Denise Barker, author + blogger + copy editor