Someone in my Twitter feed said today:

TIL starbucks put ground up insects in stuff, and milk has blood in it.

The ground up insects part is true for now, but I'm not sure about the blood-in-milk one. It sounds half-way plausible, considering that breastfeeding mothers can sometimes suffer bleeding.

A more specific example of the claim, from notmilk.com:

Also, all cows' milk contains blood! The inspectors are simply asked to keep it under certain limits. You may be horrified to learn that the USDA allows milk to contain from one to one and a half million white blood cells per millilitre. (That's only 1/30 of an ounce). If you don't already know this, I'm sorry to tell you that another way to describe white cells where they don't belong would be to call them pus cells.

Snopes says (no links due to its dodgy advertising) that the blood in milk (specifically, blood in chocolate milk) is false, but doesn't provide any specific references. Most of the other top Google hits for cow's blood milk are for anti-milk sites, user-generated content, or pages unrelated to this topic.

For convenience, assume that the claim is about the processed and government-approved milk that people in the USA drink, not what immediately comes from the cow.

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    "Ground up insects" has been widely used in food for a long time. Why are people getting upset about this? Starbucks is using widely used food additives. Ten years ago, I couldn't find a grapefruit juice that didn't contain carmine, though nowadays it is much easier to find one that doesn't. – Sam I Am Apr 20 '12 at 14:22
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    And honey is essentially bee's spit. So what? – nico Apr 20 '12 at 16:51
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    @nico isn't it actually closer to vomit? – Joshua Drake Apr 20 '12 at 19:33
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    “another way to describe them” – certainly. A wrong way. – Konrad Rudolph Apr 21 '12 at 19:36
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    Given how many people eat meat (which, no surprise, also contains blood), I'm surprised people are suddenly grossed out that their pasteurized milk contains blood components as they drink a glass of milk after easting their medium-rare steak. It should be no surprise that animal products contain animal components. – Johnny Jan 16 '14 at 22:40

We can debunk this just by analysing the claim:

  1. "White blood cells", despite their name, are the cells responsible for the immune system, and occur throughout the body (see reference number 2). Also called leukocytes, the presence of these cells is not an indication that blood (or pus) is present.
  2. The claim actually says "all cows milk contains them". So even if you milked your own pure-bred grain-fed cow in perfectly clean conditions you would still find leukocytes. This is not a contaminant, it's a perfectly normal part of milk. It's no worse than saying "milk contains fat".
  3. The math is hideously wrong here. A million cells weigh about a millionth of a gram, not a thirtieth of an ounce. So even according to the claim, only one part per million of milk is allowed to be leukocytes.

Yes I referenced Wikipedia, because this is very basic stuff, which Wikipedia is allowed for.

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    I think your 3rd point is based on a misreading. I believe the quoted claim is translating 1ml into a more familiar unit for those who don't use metric. 1 fluid ounce is, in fact, about 30ml. – Simon Apr 20 '12 at 17:37
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    @Simon I suspect the people who wrote the quoted material did so with the intent of a significant fraction of people making that error... – Dan Is Fiddling By Firelight Apr 20 '12 at 19:13
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    Note that this is also absolutely true for human milk – nico Apr 21 '12 at 12:59
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    MILK CONTAINS FAT?!?!?!!! – Konrad Rudolph Apr 21 '12 at 19:38
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    Much as I like the answer, it is incomplete without mentioning mastitis (Somatic cell count) because this is where the “pus” allegedly comes from. As far as I can see that claim is still wrong (the leukocyte count is simply elevated and bacterial screening is done separately). – Konrad Rudolph Apr 21 '12 at 19:51

"Milk contains blood" is a metonymical exaggeration for the correct idea that milk contains some of the same components as blood. The word for a whole ("blood") is wrongly being used to denote only a part ("white blood cell") giving rise something reminiscent of this:


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    It's not only wrongly being used, it is purposely being used that way to make it sound somehow "unnatural". – nico Apr 21 '12 at 12:58

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