How to identify harmful food and prevent illness

October 25, 2025 •

4 min read

An estimated 600 million people worldwide fall ill from contaminated food annually, with 420,000 resulting deaths. Learning how to identify harmful food is a critical skill for protecting your family's health and avoiding dangerous foodborne illnesses. This guide will walk you through the essential signs and practices.

Quick Summary

Recognize the signs of spoiled or contaminated food by examining appearance, texture, and odor. Interpret date labels correctly, understand cross-contamination risks, and learn essential storage and handling techniques to keep your kitchen safe.

Key Points

Visual Inspection: Look for mold, discoloration, and signs of decay, as these are often the first indicators of food spoilage.
Check Packaging: Never consume food from cans that are bulging, leaking, or deeply dented, as this could indicate a serious bacterial contamination like botulism.
Don't Trust the Sniff Test: A normal smell does not guarantee safety, as many dangerous bacteria that cause food poisoning are odorless.
Know Your Dates: Differentiate between 'Use-By' (safety) and 'Best Before' (quality) dates to avoid risks with perishable items.
Prevent Cross-Contamination: Always keep raw meat, poultry, and seafood separate from ready-to-eat foods to prevent the spread of bacteria.
Cook to Safe Temperatures: Use a food thermometer to ensure meats, poultry, and eggs are cooked thoroughly to kill any present harmful bacteria.

Your Senses Are Your First Line of Defense

Visual inspection is often the first step in determining if food is safe to eat. While some signs are obvious, others can be subtle. Pay close attention to these cues, but remember that the absence of visible signs does not guarantee safety.

Look for Visible Mold and Discoloration

Visible mold is a clear red flag. It can appear as green, white, or black fuzzy spots on a variety of foods, including bread, cheeses, and fruits. Remember that mold has threadlike roots that can penetrate deep into food, making it unsafe to simply cut off the visible portion in most cases. Discoloration is another sign. For example, fresh meat should be a vibrant red color; if it starts to turn brown or gray, it may no longer be safe to consume. Similarly, fruits and vegetables that have lost their vibrant hues or developed brown or soft spots are likely past their prime.

Inspect Packaging for Damage

Before you even open a product, check its packaging for any signs of compromise. Damaged packaging can introduce harmful bacteria. Look for:

Swollen or bulging cans: This is a sign of internal bacterial activity producing gas and can indicate the presence of Clostridium botulinum, which causes a potentially fatal illness.
Leaking or torn packages: Any hole or tear can allow contaminants to enter the food.
Damaged seals or safety buttons: If the safety button on a jar lid is up instead of down, it indicates the vacuum seal has been broken.

The Limitations of Smell and Texture

While a foul odor is a strong indicator of spoilage, relying on smell alone is a dangerous mistake. Many of the most harmful foodborne pathogens, such as Salmonella and E. coli, do not produce any noticeable smell. Therefore, food can appear and smell perfectly normal while still being contaminated. Texture also plays a role. If deli meat develops a slimy film or if vegetables become unusually mushy, it is a clear sign of spoilage.

Demystifying Food Labels and Dates

Food date labels can be confusing, but understanding the difference between Best Before and Use-By is crucial for safety. A Use-By date is a safety marker for highly perishable foods and should be strictly followed. A Best Before date, on the other hand, indicates peak quality, and food is typically safe to consume past this date as long as there are no other signs of spoilage.

Comparison of Date Labels


Feature	Best Before Date	Use-By Date
Purpose	Indicates the peak quality of the food.	Indicates when the food is no longer safe to eat.
Safety	Food is generally safe to consume after this date if stored correctly and shows no signs of spoilage.	Food should not be consumed after this date due to safety concerns.
Applicable Foods	Non-perishable items like canned goods, dried goods, frozen foods, and biscuits.	Highly perishable items such as fresh meat, poultry, seafood, and dairy products.
Rule of Thumb	Often about quality, not safety. The 'sniff test' and visual checks can be used with caution for items past this date.	A hard line for safety. Do not eat after the date has passed.

Avoiding Cross-Contamination

Cross-contamination is the transfer of harmful bacteria from one food item to another, typically from raw food to cooked or ready-to-eat food. This can happen in many ways and is a major cause of foodborne illness. Using separate cutting boards for raw meat and produce is a fundamental rule. Washing hands, utensils, and surfaces thoroughly with hot, soapy water after handling raw foods is also essential to prevent the spread of bacteria.

Key Practices for a Safer Kitchen

Following basic food safety practices can significantly reduce your risk of consuming harmful food. The World Health Organization (WHO) outlines five key principles for safer food that are easy to remember:

Keep clean: Wash your hands and surfaces often, especially after handling raw meat, poultry, and seafood.
Separate raw and cooked food: Use separate equipment and storage to prevent cross-contamination.
Cook thoroughly: Cook food to the proper internal temperature to kill harmful bacteria. A food thermometer is the only reliable way to check.
Keep food at safe temperatures: Refrigerate or freeze perishable food promptly. The danger zone is between 40°F and 140°F where bacteria multiply rapidly.
Use safe water and raw materials: Choose safe and fresh raw materials and wash fruits and vegetables under running water.

When in Doubt, Throw it Out: Conclusion

Learning how to identify harmful food is a vital part of protecting your health. By using your senses, understanding food labels, and practicing proper hygiene, you can significantly reduce the risk of foodborne illnesses. Remember that while visual and olfactory cues can alert you to spoilage, they are not foolproof indicators of safety. For truly high-risk items, trust the Use-By date, and always prioritize caution over waste. Adopting these habits will create a safer, healthier kitchen for you and your family. For more information and resources on maintaining a safe kitchen, the CDC Food Safety website offers comprehensive guidance and the latest recommendations.

Frequently Asked Questions

No, you should not rely on the 'sniff test' for safety. While a bad smell is a sign of spoilage, many harmful, disease-causing bacteria have no odor. This means food can smell and look perfectly fine but still contain pathogens that cause food poisoning.

A 'Use-By' date is a safety-based date for perishable foods, meaning you should not eat the food after this date. A 'Best Before' date is a quality-based date, indicating when the food is at its peak quality. It is typically safe to eat food past its 'Best Before' date, as long as there are no visible signs of spoilage.

Small, shallow dents are generally harmless. However, deep dents, especially those on seams, can compromise the can's seal and allow bacteria to enter. Bulging or leaking cans should always be discarded immediately, as they are a major indicator of dangerous bacterial contamination, like botulism.

No, you should never wash raw chicken or other raw meats. Washing can splash harmful bacteria, such as Salmonella and Campylobacter, onto your hands, counters, and other foods. The only way to eliminate these bacteria is by cooking the food thoroughly to the correct internal temperature.

To prevent cross-contamination, use separate cutting boards and utensils for raw meat and produce. Always wash your hands thoroughly with soap and warm water after handling raw foods. Store raw meat on the bottom shelf of your refrigerator to prevent juices from dripping onto other food items.

For soft foods like bread, soft cheese, and berries, you should throw the entire item away, as mold roots can spread invisibly throughout the food. For hard foods, like blocks of hard cheese or firm vegetables, you can cut at least one inch around and below the moldy spot, but avoid cross-contaminating your knife.

Common symptoms of food poisoning include diarrhea, stomach cramps, nausea, vomiting, and fever. Symptoms can range from mild to severe and may appear hours or days after eating contaminated food.