In Lightroom you can use the local adjustment brush and put the clarity slider to the negative side and brush this on. The beauty is you can adjust the level of negative clarity if you find your initial setting is incorrect.
The other option is to use Photoshop. Duplicate the background layer, and on this duplicated layer apply Gaussian blur. The exact amount depends on the subject, but don't over do it. Then using a layer mask remove the blur from areas such as the eyes and teeth.
A quick search on the internet will give you a more detailed explanation of the technique