Because the inflammatory process is complex its biochemistry is not yet well understood. Allergic reactions are actually harmful manifestations of the immune response causing inflammation in the affected part of the body. PGs (prostaglandins) have been implicated in the inflammatory and allergic reactions. Researchers however disagree on the precise nature of their involvement. Some researchers have demonstrated that PGs or certain ones can inhibit inflammation and hypersensitivity in both in vitro and in vivo models. Others have shown data which support the hypothesis that PGs are mediators of the inflammatory response. The problem is complicated by the fact that PGs vary in their effects depending on the species the cell or the organ system studied. Several researchers have hypothesized that PGs may influence inflammation through a feedback inhibition acting as an inflammatory agent at low concentrations and as an anti-inflammatory agent at higher concentrations.