Even if you're fanatical about your shaving technique, skin irritations can arise. This could be because you have sensitive skin that is aggravated by the act of shaving. The skin is irritated by the shaving and a day or two later you have a red rash that takes as long to disappear as it took to develop.
If your skin has been burnt by harsh elements like sun and wind, you will be especially prone to skin irritation from shaving. Do not shave damaged or sun-burnt skin, wait for 24 to 48 hours and give the skin a chance to heal.