Usually an infected cut will be very red around the cut it may hurt or feel hot or be swollen, also any yellow or greenish tint, if there are red lines running from the injury up your hand this could be sign of blood poisoning (an infection that has enter the blood stream) In the case of red lines you need to see a Dr immediately, otherwise wash it really well and put and antibiotic ointment on it 2-3x day, if it isn't better in 2-3 days or the redness or swelling increases seek medical attn
It usually will be red, tender, warm/ hot around the area and have a yellow drainage. Seek medical advice for above or if it doesn't get better in a few days. There are lots of nasty germs out there! Also depends on how you got the injury. Was it cut by an old rusty metal or an unknown object in the dirt? May need a tetanus shot...
normally you can not tell but the only way to know quickly is not that easy and is a little bit complicted that is by using a microscope because our naked eyes dont have exraordinary pupils to view sunlight rays on the infected object for the brain to see but if it is an object put it in a sterilizer nd the you ind the spot coming RED
A resolving wound will scab over and dry up and the scab will eventually fall or slough off. If your wound has not dried and scabbed over YOU MOST LIKELY have an infected wound. Seek medical attention; at the very least, wash thoroughly with an an antiseptic and then keep the wound moist with a barrier of antiseptic ointment and a bandage. Clean the wound twice daily, reapplying the antiseptic and a clean bandage each time. Nature's best way to debride a wound is honey. Google it!