Aged cheese

hard, long-aged cheeses are among the highest-histamine foods, and the longer the ageing the more histamine they hold. Young, fresh, unaged cheeses contain far less histamine.

Aged cheese is the reference tyramine food — the 'cheese effect' is named after it. Bacteria break the milk protein down over months and decarboxylate its tyrosine, so tyramine tracks ageing almost linearly: a mature cheddar or a blue can exceed 100 mg/kg while a fresh cheese sits near zero. Cooking does not destroy it, and it keeps rising in the fridge after opening. If you take an MAOI antidepressant this is the single most important food to avoid — a large portion can trigger a hypertensive crisis. Sources: EFSA Panel on Biological Hazards, Scientific Opinion on tyramine and histamine in fermented foods, EFSA Journal 2011; McCabe-Sellers et al., J Food Compos Anal 2006; Gardner et al., J Clin Psychiatry 1996.

this is where the gradient ends — a long-aged hard cheese holds about 0-0.1 g of lactose per 100 g, effectively none. Two things strip it: the whey (which carries the lactose) drains away at the curd stage, and the starter cultures eat what little stays behind over the months of ageing. The older the cheese, the less lactose. Parmesan, aged cheddar, gruyere and comte are usually fine even for people who react to milk.