What causes blackness under eyes?

I have blackness under the eyes this may sound crazy but i was in the army for 2 years and the blackness went away i think it may have something to do with the lifestyle you lead as you can expect when i was in the army i lead a healthy life style sleeping well eating healthy and a lot of fitness drinking lots of water my skin was in ace condition and no blackness but now its back so im going to experiment and lead the life i had in the army sleeping well ect ect if this works anyone with blackness under the eyes should try this. Interesting. Many specialists blame the blackness on allergies. I always observed that only the sick, the sleepless, the obese and the computer workaholics tend to get it. Maybe all of the above goes with unhealthy eating habits and that may indeed cause it. Answer In my opinion and experience, the blackness of eyes is mainly because of smoking , too much computer use and iron deficiency. If you sleep alot while eating well even then you will get black circles. So, a well balanced life, routine and diet all contribute. Also saving eyes from sun is as necessary as other factors. Use of a good sunscreen and sunglasses is a must.