Dogs usually eat facial tissues because they are bored, have pica or are simply hungry. Puppies explore their world by chewing on it and may develop a paper-eating habit for the texture or to gain their owners' attention. Pica and eating for hunger often exacerbate this problem.
Bored puppies who do not have enough exciting things to chew when they are young may resort to facial tissues and other paper products for entertainment. Puppies can't always distinguish between positive attention and negative attention from owners. Eating paper products often earns a puppy its owner's attention in the form of scolding, which is mistaken for desired attention.
Puppies with pica, a disease where the body craves non-food items, tend to have stronger tendencies to eat paper. Toilet paper and tissues are often easily accessible to puppies and satisfy their cravings. Puppies who eat facial tissues out of hunger are searching for something to fill their bellies. Facial tissues and other paper products do the job of filling them up but may have severe impact on digestive health.
After eliminating possible physical issues, the only way to keep puppies from eating paper products is to keep the products out of their reach and avoid giving them extra attention for the consumption. Puppies not trained out of this behavior may bring the problem with them into adulthood.