Why is one eye more puffy than the other? (Photo)

Asymmetry of the area under the eye can occur for several reasons.  Based on your photo it appears that yours is caused from fat protruding more under the one eye.  We often treat this with fillers to try to even contour irregularities, but there are other options available.  I would welcome you to our office in Houston for an in person evaluation if this is something you are interested in treating.

Dear Stace,It appears that your starting to develop lower lid eyelid bags as a result of periorbital fat pushing forward into the lower eyelid space. This can make a person appear tired, sick and older even when they feel fine inside. Best to seek a surgeon in your area with a specialty in Oculoplastic Surgery.Options could include temporary fillers to camouflage the fullness there vs. surgery to remove or relocate the fat in this region.I hope this was helpful. 

Eyelid puffiness can be genetic (your girdle that holds the fat behind your eye is weak), due to allergies or the first sign of the autoimmune disease like thyroid eye disease. 
A couple of options you could try:
1. Change your pillows to hypoallergenic ones
2. Sleep in an eye mask
3. try using over the counter allergy medications, flonase nasal spray twice daily alone may do the trick
Avoid:
1. Rubbing your eyes
2. Waterproof make-up that requires rubbing to get off
3. Tear drops like visine that have preservatives that can be sensitizing
Hope these help !

Hello Staceface_88,If you are starting to notice puffiness below one eye that is present all the time, this likely represents fat that is normally below the eye that is starting to push out.  When it develops in younger patients, it is usually associated with genetics (thanks mom and dad), although the aging process can also bring it on.  As you age, it will likely continue to become more noticeable.  There are several ways to treat this including using fillers to camouflage and surgery to remove it.  I would recommend you consult with a facial plastic surgeon to learn your various options.  I hope this helps and good luck.