Way back when there was Elvis and dinosaurs we learned not to put our fingers on the front of the camera lenses. If they were our camera lenses we got fuzzy, low contrast pictures with smeared details. If they were someone else's camera lenses we got socked in the ear. Either way, the front surface of the lens was sacred territory.
Not to dust. Not to mud. Not to dog noses. The schmutz still accumulated even if we did not add to it.
We learned to fasten a UV filter to the front of the lens to move this contamination one surface further. A cheaper surface, so that if we scratched it, we could replace it ourselves. But it still got dirty.
We bought special lens cleaner from Kodak until we discovered how to make our own. This commendable independence on our part is probably what killed off the company...that and their digital camera designs. I feel kind of bad about this.
To avoid this again, I now buy my lens cleaner from Giotto. They make it in small spray bottles that are packaged with a brush, a polishing cloth, and some ear-cleaning sticks. I'm pretty sure it contains some detergent, some alcohol, and some distilled water and I'l bet I could make my own, but I don't want to torpedo Giotto or the wholesalers.
Out in the field where one encounters dog noses I carry the Lens CLeanse one-time pre-pack cleaners. They are powerful, but gentle and can cope with most grease or dirt contamination very well. You can get them in packets of 12 if you own a pack of beagles.