  The hydrogen atom under the pressure of a spherical penetrable confinement
potential of a decreasing radius $r_{0}$ is explored, as a case study. A novel
counter-intuitive effect of atomic swelling rather than shrinking with
decreasing $r_{0}$ is unraveled, when $r_{0}$ reaches, and remains smaller
than, a certain critical value. Upon swelling, the size of the atom is shown to
increase by an order of magnitude, or more, compared to the size of the free
atom. Examples of changes of photoabsorption properties of confined hydrogen
atom upon its swelling are uncovered and demonstrated.
