Mayonnaise is a creamy emulsion of oil, egg yolk, and an acidic liquid like vinegar or lemon juice. The concern during pregnancy stems from the traditional use of raw egg yolks, which can harbor harmful bacteria. Uncooked eggs pose a risk to both the pregnant individual and the developing fetus. The safety of this condiment depends entirely on the preparation method and the source of the product.
Commercial Versus Homemade Mayonnaise
The primary distinction for safety lies in whether the eggs used in the mayonnaise are pasteurized. Pasteurization is a heat treatment process that destroys pathogenic microorganisms, such as Salmonella. Store-bought, commercial mayonnaise is overwhelmingly made with pasteurized eggs, making it generally safe for pregnant individuals to consume. Major manufacturers follow strict safety guidelines and often include acidic ingredients like vinegar, which further inhibit bacterial growth. Because of these controls, a jar of mayonnaise purchased from a standard supermarket shelf presents a low risk of foodborne illness.
Conversely, homemade, deli-made, or fresh restaurant mayonnaise is considered high-risk because it frequently relies on unpasteurized, raw egg yolks. Unless you can explicitly confirm that pasteurized eggs were used, it is prudent to avoid any mayonnaise that is not commercially produced and sealed. This caution extends to sauces where the mayonnaise base might be prepared fresh on-site.
Why Foodborne Illnesses Pose a Specific Danger
The avoidance of raw-egg products is a direct defense against foodborne bacteria, particularly Salmonella enterica and Listeria monocytogenes. Pregnancy causes hormonal changes that suppress the maternal immune system, making expectant mothers more susceptible to these pathogens. This increased vulnerability means that a bacterial exposure that might cause a mild illness in a non-pregnant adult can lead to a more severe outcome during gestation.
Infection with Listeria monocytogenes, known as listeriosis, is a specific concern, as pregnant women are up to 20 times more likely to contract it than the general healthy population. Listeriosis can manifest with mild, flu-like symptoms in the mother, or sometimes no symptoms at all. However, the bacteria can cross the placenta, leading to serious fetal complications such as miscarriage, stillbirth, and preterm labor. While Salmonella infection is not more common in pregnancy, the illness it causes can be more severe, with symptoms including fever, severe vomiting, and diarrhea. A high maternal fever and dehydration pose risks to the fetus.
Practical Guidelines for Storage and Consumption
Even a commercially safe jar of mayonnaise requires diligent handling once it is opened. Proper refrigeration is mandatory to keep the product out of the temperature danger zone, which is between 40°F and 140°F (4.4°C and 60°C). This range allows for the rapid multiplication of bacteria that may have been introduced during serving or from cross-contamination.
Once a jar of mayonnaise is opened, it must be kept tightly closed and refrigerated at all times. A general rule is to discard any mayonnaise that has been left out at room temperature for two hours or longer. This includes dishes like potato salad or coleslaw prepared with commercial mayonnaise, as the risk increases when the product is mixed with other ingredients. Checking the expiration or “best by” date is also important, as Listeria bacteria can still grow slowly even in refrigerated conditions.
Related Condiments and Sauces to Approach with Caution
The principle of avoiding unpasteurized raw eggs extends beyond standard mayonnaise to a range of other condiments and sauces. Many classic recipes for dressings and sauces are traditionally made with raw eggs and should be treated with the same caution as homemade mayonnaise. These include hollandaise sauce, aioli, and traditional Caesar dressing, which uses raw egg yolk for its creamy texture. Freshly prepared sauces like béarnaise and certain restaurant salad dressings should also be avoided unless their use of pasteurized eggs can be confirmed. Commercial, bottled versions of these products are usually safe because they are made with pasteurized ingredients, but fresh, artisanal, or restaurant preparations should be approached with skepticism.