The full quantum statistical theory of the vertical-cavity surface-emitting laser (VCSEL) is constructed for arbitrary relations between frequency parameters. In our approach we follow Hermier et al (2002 Phys. Rev. A 65 053825) and Golubev et al (2004 Phys. Rev. A at press; Preprint quant-ph/0407006) and formulate the theory in the form of quantum Langevin equations. For detailed analysis the theory is applied to lasers with equally-lived laser levels. Spectral densities of the Stokes parameter fluctuations are obtained in explicit analytical form. A role of physical phenomena such as spin-flip and optical anisotropy (linear birefringence and linear dichroism) in semiconductor crystals is discussed. It is shown that random sub-level electron distributions do not worsen shot noise reduction efficiency. Comparing our results with the phenomenological ones (Mulet et al 2001 Phys. Rev. A 64 023817), the serious differences are disclosed. The reasons for these differences are explained.