There are a few potential causes of this sensitivity, however if the symptoms persist or worsen you will need to go see your doctor
to help you figure it out definitively.
First, it is possible that the skin has become irritated from overlying clothing. This is more common in hot weather when the skin is sweaty. Although the skin is usually reddened, this is not always the case. If you have recently started using a new fabric or if your clothing is tight, this might be what is going on.
Another potential cause would be the start of a case of shingles. Shingles is a reactivation of the chicken pox virus. It often occurs in times of stress or illness
. Before the red blisters appear, there is often a strange sensitivity or tingling sensation in the skin. Shingles reactivations tend only to affect one half of the body, so if the sensitivity you are experiencing is on both sides of the rib cage then this is unlikely.
Finally it is possible that you have a minor strain or sprain of the muscles or joints of the rib cage. If you press on the area and the sensation is worse, this is more likely.
Please talk to your primary care doctor
if things do not improve.