Hi Anxi, The BioSURE HIV self-tests is a lateral flow strip that uses technology similar to a pregnancy test. The test strip is sprayed with synthetic peptides that represent the HIV antigens. When the blood travels along the solid phase membrane strip, if antibodies are present, the test line and control line will be visible and show the two lines. If no antibodies are present in the blood, the single control line will show. The BioSURE self-test has a built in sample control line, that shows whether your test has been performed properly. If you do not receive a control line, your test is invalid. There is no harm in touching or scratching the strip, the antigens sprayed onto the strip cannot harm you. Kindest regards, Becky, BioSURE UK LTD