Over time your calculation and intuition will likely decrease, but your general knowledge about chess shoudln't change.
If you have extensive opening knowledge, I suppose you'd start to forget it, but it's hard to say how much you'd forget in just 1 month.
Playing to much chess can make you crazzy and your chess standerd wil go down if do not rest for a whille during this time i sugest you spend time doing some other activeties ,but if you feel that like practicesing your chess during your time off from playing, I sugest doing some chess puzzles just for 30 min each day to keep in shape, but sometimes a long break is all that is needed to improve your chess.
Ohh i see,,thanks for all of your advice 
My bullet and blitz game decreases but my 30 mins and online chess is still okay,,nothing change :)
Does it decrease?
A little oxidation which results in a little rust. Stay away a year or more and there will be alot of rust. Chess knowledge won't decrease but you cannot recall it as easily. You have to get back in shape.
nothing will happen. as long as you celebrate melon day appropriately.
THANKS TRANSPO :)
If i take time off, I find it takes me a while and a good few games before I can really get back into a stride.
Hence why I proactice on chess computers when I start to play again...so as to try and minimise damage to my score...whether that works or not is usually another thing
Probably the stronger you are---the less likely it will effect you. Fischer didnt play a serious game in 20 years and came back and played a former worlds champion who had played steadily those 20 years---and won 10-5.
What was Fischer doing those 20 years? Adolph Anderssen said--- It is impossible to keep one's skill in a showcase, like a jewel. – (on the effects of not playing for a period of time).
I wonder what the odds were on the match ---I would think that Spassky would have been favored. After all, Fischer put his skill in a showcase, like a jewel. and everyone knows---you cant do that!
a month isn't that long.I remember when I took a 10 month hiatus last year it didn't take more than a week to shake off the rust.
Does it decrease?
I think you may even increase in some situations. if you play 25 games with white and you play the same opening each time. you may start to play two or more moves without thinking because you think you have analyzed the position - no need to look at that move anymore - it must be best because I already looked at it 5 times.
By taking a break you may look at your openings with "new eyes" and may stop automatic moves that might not be the best afterall.
Does it decrease?