What’s the cause of these sudden under eye bags at 25 years? (Photos)

Weight loss can cause volume loss in the face.  If they have come on suddenly they could be related to allergies.  Most times the cause is genetics.  The good news is they respond well to treatment with fillers.  This is performed in the office and the results last up to one year.  See an expert injector in your area to learn more.

Under eye bags can be permanently corrected with surgery or temporarily camouflaged with fillers (Restylane, Belotero, Volbella) which can also help nasolabial folds.There are great non-surgical options to fill in under eye depressions and hollowness. Using dermal fillers, a liquid eye-lift can be performed. A dermal filler such as Restylane would be placed in the cheek and tear trough to hide the depression or bag underneath your eye. 
Surgery would require a fat-repositioning lower lid blepharoplasty. In this surgical procedure, fat from the eye area is moved into the tear trough depression filling the actual depression. 
I hope this helps!