Why is it bad to make eye contact with dogs?

With wild dogs/wolves, prolonged eye contact is seen as a challenge or a threat, but, with domesticated dogs, it does depend on the dog's personality as well as the person. There was a study conducted by researchers in Japan earlier in 2015 suggesting that eye contact between a dog and his/her owner can cause increased levels of oxytocin, the "hug hormone," in both parties. We can't know what exactly is going on in a dog's head, but if you and your dog have a healthy bond with one another, prolonged eye contact from your dog can be compared to them giving you a hug.

Here's an interesting article from the New York Times that goes into more detail about the research:

http://well.blogs.nytimes.com/2015/04/16/the-look-of-love-is-in-the-dogs-eyes/?_r=0 (http://well.blogs.nytimes.com/2015/04...)

It really depends on the dog and how you're looking at them, just like people. We've selectively bred dogs over generations to respond to and work with people, so unlike their wild counterparts, many dogs enjoy and seek out eye contact with people. However, maintaining eye contact can be confrontational, especially to a dog you aren't familiar with or if your body posture is otherwise threatening.

Likewise, eye contact from dogs can run the gamut from a friendly attempt to engage you to a challenge or threat. You have to consider the total picture rather than just one detail. If the dog's eyes appear bright, their posture is loose and flowing or bouncy, their facial muscles are relaxed, they're probably enjoying the interaction. If you're looking at a dog and they start giving you big blinks, looking away/turning their head away, licking their lips (in the absence of food), assuming a hunched posture, yawning, or just looking overall uncomfortable, then you may be making them a little uncomfortable, and should probably give them some space to show you mean them no harm.