Apple’s Support Website is the bottom line when you come to iMac (or any Mac for that matter) screen cleaning. Here they tell you their method for cleaning all their devices. It is quite thorough and I highly recommend you read it. But, I wanted to relate my own experiences with cleaning my iMacs (and laptops over the years).
Apple recommends using plain water to clean most of their devices. They caution you to not spray water directly on the device itself, but onto a lint free cloth. The only thing I would say about this is most of our water supply these days contains all kinds of stuff (chlorine anyone) that may not be too good for your computer screen. In my research over the years I have discovered that many people use distilled water and a lint free cloth (you can get lint free cloths at Amazon) to clean their Mac screens. Now I would say that would good if I was going to go the water route.
However, I have used a product called Omnicleanz for years now to clean the screens of my devices including my iPhone, iPad and various laptops. It is alcohol and solvent free. It is very gentle and does a great job of cleaning. You can buy other “screen cleaners” online, but you must be sure they do not have alcohol, ammonia or solvents in them.
No matter what you use to clean your iMac, one thing is a constant. You must use some elbow grease to make it work. I don’t know if you have noticed this, but no matter what you use it tends to leave kind of a film on the glass (screen). Many cleaners claim to be “streak free” and they are, but this kind of film still seems to happen. You really have to hold the Mac steady and “rub out” the entire screen to get that film off. This process is a bit of a pain, but yields great results in the long run. Oh yes, Apple recommends having the machine shut down and unplugged. That is usually the way I do it.
I probably do this cleaning process with Omnicleanz every 4-6 weeks on my iMac. No, I don’t touch the screen and make marks on it, but it just seems to get cruddy after a while. I will dust it off maybe once a week with a lint free cloth, but the actual cleaning is only once a month or so.
Apple has a product called iKlear that they recommend but I have found it streaks pretty badly. I do use iKlear to clean the outside of my devices sometimes, but prefer Omnicleanz for the screen.
What ever way you choose to do your cleaning you will need a lint free cloth (no paper towels or rags) and you will need to work at it a little bit. A clean iMac screen can yield great dividends in your overall computing experience.