The invention relates to a high pressure homogenizer (1) for flowable substances charged with particles, having a high pressure chamber (2) and a homogenizer unit (3) that is located fluidically downstream thereof and, by swirling, expands the fluid to be homogenized which has previously been brought to a pressure of more than 500 bar in the high pressure chamber (2), and a plunger pump (4) associated with the homogenizer unit (3), the plunger (5) of which plunger pump pressurizes the high pressure chamber (2), wherein the high pressure homogenizer (1) has a low pressure chamber (7) which surrounds the plunger shaft (6) to cool the plunger (5) and which has an operating pressure of PN ≤ 25 bar, wherein the low pressure chamber (7) and the high pressure chamber (2) are separated from each other by a seal (8) which is penetrated by the plunger (5), the seal (8) being a throttle gap which is formed between the plunger shaft (6) and a bushing (9) that does not contact the plunger shaft (6), the ratio S/L of the length (L) to the radial annular gap height (S) of the throttle gap being ≤ 0.0015.