Lactose is the naturally occurring sugar in milk. During the cheese making process, most of the lactose is drained off with the whey (a liquid portion). Cheese, therefore, contains very little lactose.
According to Allergy UK:
“Lactose intolerance is not the same as a milk or dairy allergy. Food allergies are caused by a reaction to a food by your immune system, causing symptoms such as a rash, wheezing and itching.
If you’re allergic to something, even a tiny particle can be enough to trigger a reaction, while most people with lactose intolerance can still consume small amounts of lactose without experiencing any problems (although this varies from person to person).”
Cheese with trace levels (less than 0.5 gram lactose): Natural, aged cheese (such as Cheddar, Parmesan and Swiss) can be digested by many people with lactose intolerance. The small amount of lactose that remains in the curd is changed to lactic acid during ripening (ageing).
Cheese with low levels (less than 5 grams lactose): Fresh unripened cheese (such as mozzarella, cream cheese and ricotta) are not aged. Only part of the lactose that remains in the curd has a chance to convert to lactic acid. Cottage cheese, also a fresh unripened cheese, generally has additional milk or cream mixed with the curd. Therefore, fresh cheeses contain more lactose than aged cheeses.
Processed cheese foods and cheese spreads are made by melting natural cheese to stop the ageing process and then adding other ingredients, including whey or milk. Cheese foods and cheese spreads contain lactose.
So if you are lactose intolerant, look for aged, rather than younger, cheeses, with sugar under 5 grams per serving. Dairy guru Steve Carper also suggests another rule of thumb: The higher the fat content, usually the lower the lactose levels. He also has a big list of dairy products’ lactose percentages for your reference, while IBS Free has another (PDF) list with the lactose amounts in grams.