We show in this article how an electric and magnetic dipolar particle has its polarisability that is changed in a non-vacuum environment. This result is used to calculate the signal obtained by an apertureless Scanning Near-Field Optical Microscope (SNOM) when the tip is a dipolar particle. This signal only depends on the field without tip and on the particle and surface optical properties. We apply our theory results to the case where the surface excited by a polariton and to the case where it is thermally excited. In this last situation we show that the measure obtained is a local surface spectroscopy. We specify the practical situations where the signal detected by the SNOM can be related to the electromagnetic Local Density of States (LDOS). We finally examine the cooling rate of a dipolar particle is modified when the particle is approached to a surface and how a heated particle can be used to make a local spectroscopy