We discuss the problem of static chaos in spin glasses. In the case of magnetic-field perturbations, we propose a scaling theory for the spin-glass phase. Using the mean-field approach we argue that sorne pure states are suppressed by the magnetic field and their free-energy cost is determined by the finite­temperature fixed-point exponents. In this framework, numerical results suggest that mean-field chaos exponents are probably exact in finite dimensions. If we use the droplet approach, numerical results sug­gest that the zero-temperature fixed-point exponent 0 is very close to ( d - 3) /2. In both approaches d = 3 is the lower critica! dimension in agreement with recent numerical simulations.