The dietary guideline advising pregnant individuals to avoid soft cheeses is based on an elevated risk posed by specific foodborne bacteria. This restriction mitigates a rare but serious health concern linked to the characteristics of these dairy products. The concern is tied to the potential for bacterial growth within the cheese’s structure and the unique vulnerability of the pregnant immune system.
The Specific Health Concern: Listeriosis
The primary concern with soft cheeses is contamination with the bacterium Listeria monocytogenes, which causes the foodborne illness listeriosis. This infection is particularly dangerous during gestation because pregnancy-related hormonal changes suppress immunity. Expectant mothers are approximately 10 to 20 times more susceptible to contracting listeriosis than the general healthy adult population.
The infection may present as a mild, flu-like illness, or sometimes with no symptoms, making early detection difficult. However, the bacteria can cross the placental barrier and severely affect the developing fetus, leading to miscarriage, stillbirth, or premature delivery.
Newborns who contract the infection may develop serious conditions such as sepsis or meningitis. The consequences for the baby can include long-term health problems or, in the most severe cases, death.
Distinguishing Safe and Unsafe Cheeses
The risk level of a cheese is determined by two factors: the use of pasteurized milk and the cheese’s physical characteristics, such as moisture content and acidity. Pasteurization is a heating process that kills harmful bacteria, including Listeria, present in raw milk. Any cheese made with unpasteurized milk should be avoided immediately, regardless of its softness.
Soft cheeses still pose a risk even if made with pasteurized milk, as Listeria can be introduced through contamination after pasteurization, such as during aging or packaging. The high moisture content, lower salt, and lower acidity of soft, mold-ripened cheeses provide an ideal environment for Listeria to multiply, even under refrigeration. Examples include Brie, Camembert, Feta, and Blue cheeses.
In contrast, hard cheeses like Cheddar, Parmesan, and Swiss are safe because their low moisture and high acidity do not support bacterial growth. Soft cheeses that are not mold-ripened, such as cream cheese, cottage cheese, and mozzarella, are also safe to consume. These varieties are safe only if they are clearly labeled as being made with pasteurized milk.
Practical Steps for Risk Reduction
The risk associated with soft cheeses can be eliminated if the food is heated correctly, as Listeria is destroyed by heat. Restricted soft cheeses, such as Brie or Blue cheese, become safe to eat if they are cooked until steaming hot throughout. This means a baked Camembert or soft cheese melted onto a pizza or casserole is safe for consumption. The internal temperature must be high enough to ensure the bacteria is killed in every part of the food.
General food safety practices are important for preventing all foodborne illnesses. Pregnant individuals should avoid cross-contamination by washing hands, utensils, and surfaces thoroughly after handling uncooked food. Ready-to-eat foods, like leftovers or deli meats, should also be reheated to steaming hot before eating.
If an individual believes they have consumed a contaminated product or experiences flu-like symptoms after eating a high-risk food, they should contact a healthcare provider immediately. Although listeriosis is rare, prompt diagnosis and antibiotic treatment can be administered during pregnancy to reduce the severity of the infection for the fetus.