The thought that occurs to me would be...perhaps it is something like not rinsing the area thoroughly after washing (soap or even the baking soda) or brushing teeth.
I say this because I had a similar problem around the hairline; it was very easy to apply soap, lotion, exfoliant etc. in the area, but forget to rinse as thoroughly as it needs. Then I'd also be surprised at the break-out. The break-outs ended after I began ensuring all of the products were completely removed.