Is it dangerous to do solarium once a week for about a month before summer season?

Maybe: I am assuming you are referring to tanning bed? Once a week at the most. Melanocytes release their melanin after 12 minutes of exposure. All time after that equates to skin damage. Areas of face are more susceptible. Though some consider all tanning not safe, if you must restricting to 12 minutes in regular bed, 8 minutes high pressure and cover face.