We consider fracture growth controlled by fluid diffusion into the fracture. If the fluid is accumulated inside the fracture, after some incubation period, it starts growing under the pressure of the accumulated fluid. An important example is given by hydrogen induced cracking. Hydrogen absorbed by a metal is typically dissolved in the lattice in the proton form. Some of the protons reach the surface of a pre-existing or freshly created cracks where they recombinate with electrons and form molecular hydrogen in the crack cavity. Because usually the molecular form of hydrogen is thermodynamically more stable, this process leads to accumulation of gas hydrogen inside the crack. Then, the fracture often takes place even in the absence of any external loading, that is, only under the excessive hydrogen pressure. Another example is given by heating of water saturated rock. If due to the heat diffusion, the water evaporates/boils inside the cracks, the pressure exerted by the vapor can cause the cracks to propagate, increasing the crack sizes by orders of magnitude.