During puberty, the activity of sebaceous gland, sweat gland increases leading to release of more oil, sweat which gets collected in pores of skin thus pores get blocked. Bacteria grow there leading to the development of pimples. So we have to clean our face at regular interval to make our face sweat and oil free. We can use face wash which will remove oil and sweat thus pores on skin gets opened. So bacteria cannot grow and there will be no pimples or acne.