Derald Wing Sue et al. (2007) posit that micro-aggression racism is:

a contemporary form of racism that is invisible, unintentional, subtle in nature, and typically outside the levels of conscious awareness, but it creates a hostile and invalidating climate nonetheless.  According to Sue and Colleagues, the cumulative of micro-aggressions may be just as harmful as outright racism, although more research is needed in this regard.

Source: Ghaffar-Kucher, A. (2011).  The religification of Pakistani-American Youth.  American Educational Research Journal.  Pg. 26.

Available at: http://aer.sagepub.com/content/early/2011/08/02/0002831211414858