All research activities that involve living human subjects or biospecimens (including genetic data and, in some cases, biospecimens from deceased subjects) require IRB review and approval before research can begin. Not doing so is considered unethical and, in some cases, illegal. The most difficult question in determining if a project requires IRB review is whether it constitutes "research" as defined by the Office of Human Research Protection (OHRP). The OHRP discourages researchers from making this determination on their own.
The OHRP provides basic guidance here: OHRP Decision Charts