1) Your skin is probably very sensitive.
Check the instructions. Stick to the course outlined for persons with a very sensitive skin.
If you think the sessions are still too long for you, you could shorten them by five minutes for each side of your body.
2) Medication and certain cosmetics may cause side effects, such as skin irritation.
Always remove cosmetics before using the appliance. If you are on medication, read the leaflet provided with your medication to check if it increases the sensitivity to UV or ask your pharmacist or doctor in case of doubt.