Unveiling the mysteries of dark spots in eggs: A concern for food safety?


    5th June 2024 – (Taipei) In recent discussions on social media platforms, including a post by a Taiwanese Facebook user, concerns have been raised over the appearance of black spots within eggs, sparking fears over potential food safety issues. These observations have led to a deeper exploration into the nature and implications of these spots.

    The black spots, often seen as alarming and unusual by consumers, can manifest under various circumstances. Contrary to the belief that these are indicators of fertilisation, experts clarify that such spots are not embryonic but rather result from conditions during the egg-laying process. The Taiwan Agriculture Council explains that true fertilised eggs feature a network-like distribution of blood vessels, which differs significantly from the sporadic spotting observed.

    These spots, sometimes also appearing as blood clots, are usually caused by bleeding in the hen’s oviduct during the ovulation cycle. Consequently, eggs with such imperfections are referred to as ‘blood spot eggs’ or ‘foreign material eggs’. Research indicates that such abnormalities are found in approximately 18% of red-shelled eggs, compared to a mere 0.5% in white-shelled eggs. Importantly, these do not compromise food safety and eggs remain safe to eat, though they may have a reduced shelf life.

    Situations and implications of black spots in eggs

    1. Cooked yolk blackening: Some users have reported black spots appearing in the yolks of hard-boiled eggs. Typically, this discolouration around the yolk’s periphery is attributed to overcooking, leading to a chemical reaction between sulfur-bearing amino acids and iron within the yolk, forming ferrous sulfide. Despite its sinister appearance, this poses no food safety risk.
    2. Surface speckles on egg whites: This scenario is particularly disturbing when visualised but is generally harmless. It often occurs when eggs are cooked in iron pots with vinegar added, promoting a reaction where iron leached from the pot interacts with sulfur-containing amino acids in the egg white.
    3. Black spots on the inner shell: The most concerning scenario involves black spots on the inner surface of the eggshell, often visible upon cracking the egg open. This usually indicates mould growth, which can occur if the eggshell exhibits visible cracks or mould spots. Consumption of such eggs is strongly discouraged as they are likely spoiled and may lead to health issues including nausea and abdominal pain.

    While the presence of black spots in eggs can be off-putting, it is crucial to discern their nature and location to assess the potential risks. Most instances do not pose a threat to health, except where mould is present, warranting caution and ensuring that such eggs are not consumed. This understanding helps demystify the concerns around these peculiar egg anomalies, reinstating confidence in the safety of commonly consumed eggs.