Hi, I'm wondering how often I should buy skin lightening products cause I've barely gone out for like 6 years now but only my body, legs, and feet are lighter, my face and arms are darker. I usually stay at home and work on the computer and only go outside to meet some friends or get groceries maybe once or twice a week. Do skin lightening products last forever after one use or do I continuously have to buy it cause the skin lightening products here are expensive and I can't afford to buy them like every week.