Does Heating Milk Make It Unhealthy? Unpacking the Myths

November 3, 2025 •

4 min read

According to one survey, a significant number of people in certain regions mistakenly believe boiling milk enhances its nutritional value. This widespread habit raises a critical question for many: does heating milk make it unhealthy? While heating affects milk's nutritional profile, it isn't necessarily a bad practice and depends heavily on the type of milk and the temperature used.

Quick Summary

Heating milk modifies its nutritional composition, particularly reducing heat-sensitive vitamins and altering proteins. The impact varies based on the milk type (raw or pasteurized) and the temperature reached. While nutrient loss occurs with high heat, boiling is a crucial safety step for raw milk and can offer some digestive benefits for certain individuals.

Key Points

Boiling reduces certain vitamins: Heat-sensitive water-soluble vitamins, particularly B vitamins and folate, are reduced when milk is boiled.
Pasteurized milk does not need boiling for safety: Commercially available milk is already pasteurized, a process that makes it safe to drink directly from the carton.
Raw milk must be boiled: To eliminate dangerous bacteria and prevent foodborne illnesses, raw, unpasteurized milk must be heated to a boiling point.
Heat affects milk proteins: Boiling denatures whey protein, which can alter its structure and potentially affect digestibility for some, but does not significantly reduce overall protein content.
Minerals like calcium remain stable: The mineral content of milk, including calcium and phosphorus, is largely unaffected by heat.
Overheating causes taste and texture changes: Rapid or prolonged boiling can cause milk to scorch, changing its flavor and creating an undesirable skin on top.
Reheating milk is not recommended: Repeatedly heating milk can promote bacterial growth and significantly degrade its taste and texture.

The Purpose of Heating Milk

In many cultures, boiling milk before consumption is a longstanding tradition. For raw, unpasteurized milk, this practice is a critical food safety measure. Raw milk can harbor harmful bacteria like E. coli and Salmonella, which boiling effectively eliminates. For store-bought, commercially produced milk, however, this step is redundant. Commercial milk has already undergone pasteurization—a controlled heat-treatment process (e.g., 71.7°C for 15 seconds) designed to kill pathogens without drastically affecting nutrients. Therefore, unless you are consuming raw milk, the need to boil for safety is nonexistent.

The Nutritional Impact of Heat

When milk is heated, especially to a full boil, its chemical structure changes, affecting various components differently. The extent of this change depends on the temperature and duration of heating.

Effects on Vitamins

Milk contains both heat-sensitive and heat-stable vitamins. The water-soluble B vitamins are particularly vulnerable to degradation with heat exposure.

B Vitamins (B1, B6, B9, B12): Studies show that boiling can reduce levels of B vitamins by a significant percentage. For instance, riboflavin (B2) can drop by 27%, and folic acid (B9) by 36%. However, since milk is not the primary source of all B vitamins for most people, the overall dietary impact is often minor, with the exception of riboflavin.
Vitamin A and D: These fat-soluble vitamins are relatively stable and withstand the heat of boiling with minimal loss.

Protein and Fat Changes

Milk's protein composition consists mainly of whey (about 20%) and casein (about 80%).

Whey Protein: This protein is heat-sensitive and will denature, or change its structure, when heated. While this can affect its digestibility for some, it doesn't necessarily reduce the overall protein quantity.
Casein Protein: The larger casein micelles are much more heat-stable and remain largely intact even after boiling.
Fat Composition: The overall fat content remains stable, but some long-chain fats can convert into shorter-chain and medium-chain fats. Some evidence suggests these shorter-chain fats may offer benefits for gut health.

Digestibility and Allergies

Heating milk can have a nuanced effect on digestion and allergic reactions. For people with a cow's milk protein allergy, the heat-induced denaturation of whey proteins can alter their structure enough that the immune system no longer recognizes them as allergens. This is why some people with milk allergies can tolerate cooked milk products. However, this is not a universal rule, and boiling milk does not reduce the allergenicity of casein. In terms of lactose intolerance, boiling milk does not significantly reduce the lactose content, so it is not an effective remedy.

Potential Benefits and Drawbacks

Benefits:

Safety for Raw Milk: Boiling is essential to kill potentially harmful bacteria in raw milk.
Improved Digestion (for some): The denaturing of whey protein can sometimes make milk easier to digest for certain individuals.
Extended Shelf Life (for raw milk): The heat process extends the life of unpasteurized milk by killing spoilage microorganisms.
Taste Alteration: Some prefer the slightly different, sweeter taste of boiled milk, which is a result of the Maillard reaction.

Drawbacks:

Loss of Vitamins: Heat-sensitive vitamins, especially B vitamins and folate, are lost to varying degrees.
Reduced Protein Retention: While protein is not lost, high heat can cause structural changes that result in less protein being retained after digestion.
Change in Texture and Flavor: Boiling can lead to a 'cooked' flavor and the formation of a skin, which some people find unappealing.
Slight Reduction in Calcium Bioavailability: Extremely high temperatures, like ultra-pasteurization, may affect calcium bioavailability, though normal boiling has a minimal effect on the total amount.

Proper Heating Methods

To minimize nutrient loss while heating milk, especially for pasteurized products, consider these tips:

Gentle Heat: Use a medium-low flame and heat slowly, stirring occasionally, to prevent scorching or curdling.
Avoid Boiling: For pasteurized milk, simply warming it to your desired temperature is sufficient. A full, rolling boil is unnecessary and increases nutrient loss.
No Reheating: Avoid reheating milk that has already been heated once, especially in commercial settings. The repeated temperature change can promote bacterial growth and affect taste.
Use a Thermometer: For recipes or specific purposes, using a thermometer can ensure you reach the target temperature without overheating.

Conclusion: Does heating milk make it unhealthy?

Ultimately, heating milk does not make it inherently unhealthy, but it does change its nutritional profile. For pasteurized milk, the benefit of gentle warming is taste and preference, not safety, and it results in minimal nutritional impact. Boiling raw milk is a necessary safety step, and the health gains from avoiding pathogens outweigh the minor losses of heat-sensitive vitamins. Understanding the different effects of heat allows consumers to make an informed choice based on their milk type, health needs, and preferences.


Feature	Boiled Milk (Pasteurized)	Unheated Milk (Pasteurized)
Nutrient Loss (Vitamins)	Some reduction, especially in water-soluble B vitamins and folate.	Minimal to none; retains full vitamin content.
Protein Structure	Whey protein denatures; may affect digestibility for some.	Maintains original protein structure.
Digestibility	Can be easier for some with sensitivities to digest due to altered proteins.	Contains native enzymes and proteins, which some find more challenging.
Food Safety	Unnecessary for safety as it is already pasteurized, but will kill any contaminants added after opening.	Already safe for consumption when fresh; proper refrigeration is key.
Shelf Life	No significant extension; still requires refrigeration after opening.	Dependent on best-by date and refrigeration.
Taste & Texture	May have a sweeter, 'cooked' flavor and a skin may form.	Natural, unaltered flavor and creamy mouthfeel.

For more in-depth information, you can read the comprehensive guide from Healthline on boiled milk.

Frequently Asked Questions

Neither hot nor cold milk is definitively 'better,' as both are nutritionally similar. The choice depends on personal preference and desired effects. For example, some find warm milk soothing before bed, while cold milk can be refreshing during the day.

No, boiling milk does not destroy all its nutrients. While some water-soluble vitamins like B vitamins and folate are reduced, fat-soluble vitamins (A, D) and minerals like calcium are heat-stable and remain largely intact.

No, boiling pasteurized milk is not necessary for safety. It has already undergone a heat-treatment process to eliminate harmful bacteria and is safe for consumption directly from the package.

No, reheating milk multiple times is not recommended. It can affect the milk's texture and taste, potentially encouraging bacterial growth, especially if it was left in the temperature 'danger zone'.

Heating milk does not significantly affect its calcium content. Minerals are heat-stable, and studies show that boiling only causes minimal or no reduction in total calcium.

For some people with mild milk sensitivities, boiling can make milk easier to digest. This is because the heat denatures whey proteins, altering their structure. However, it does not significantly impact lactose and is not a reliable solution for lactose intolerance.

The skin that forms on boiled milk is a result of protein denaturation and fat coalescence. As milk is heated, the proteins on the surface coagulate and combine with fat particles, forming a film that is completely safe to eat.