Smart phone is becoming an important part of our lives; howerver, it also has many disadvantages. First, use too much smart phone can cause physical and psychological problems. These are problems affecting the brain, eyes, musculoskeletal, obesity, depression… Second, use too much smart phone causes: dry eyes, eyestrain, blurred or red eyes, myopia and astigmatism,… Third, phone screens emit blue light, which inhibits the production of the hormone melatonin in the brain. This is the body's sleep regulator. From there, sleep and the body's circadian rhythms are disrupted. And there are many harmful effects of smartphones such as depression, joint damage, obesity, memory impairment,... Using a smartphone is not bad, but we need to know how to use it properly.