(Slate) - The holidays are all about extended family, which means, by necessity, they’re also all about alcohol. But what if you’re a nursing mom? On the one hand, you’ve probably been told by your friends to start drinking Guinness, based on the popular notion that dark beer can boost milk supply. But your parenting books almost certainly tell you the opposite—that you should be very careful about imbibing alcohol as a nursing mom because it seeps into breast milk and thus into your baby and could pose various risks. The popular parenting website WhatToExpect.com, for instance, advises moms to have only one drink per sitting, occasionally, on a full stomach, and to always wait two to three hours per drink before nursing.

So what’s the deal? As a nursing mom myself, I wanted to find out the truth before I come face to face with a punch bowl full of eggnog. Although there isn’t a ton of research on the issue, it seems clear that knocking back a few won’t help your milk supply (and it might in fact do the opposite), but that doing so won’t knock your baby out, either. We should dispose of that horrible phrase pumping and dumping, too, because—hooray!—moms never need to do it.

Let’s start with some basic physiology. When you sip a glass of mulled wine, the alcohol moves from your stomach to your intestines and into your blood. It also passes into breast milk in approximately the same concentration—in other words, when your blood alcohol concentration is 0.08 percent, alcohol is in your milk at a 0.08 percent concentration, too. These concentrations peak about 30 to 45 minutes after you’ve had your glass, and then they both start to drop as your body breaks the wine down. So instead of having to throw your milk away after you’ve been drinking (“pump and dump”), you simply need to wait. Once you’ve sobered up, your milk will be alcohol-free again.

But even if you’ve refilled your glass a few times, there is very, very little alcohol in your milk—and very little ingested by your baby. If a 150-pound nursing mom downs four alcoholic drinks—say, four 5-ounce glasses of table wine—and then breast-feeds her 13-pound baby 4 ounces of milk when she’s at her tipsiest, her baby will end up with a blood alcohol concentration of 0.0038 percent—the same blood alcohol concentration her mom would have after consuming a mere 1.5 ounces of Bud Light (one-eighth of a 12-ounce bottle). Babies break down alcohol more slowly than adults do, but since they consume so little alcohol from breast milk in the first place, this difference “should have no clinical significance,” researchers concluded in a recent research review on the topic. Ultimately, there is a higher concentration of alcohol in some fruit juices—which can contain up to 0.1 percent alcohol due to fermentation of the sugars—than there is in the breast milk of a tipsy nursing mom. (Importantly, though, don’t confuse drinking while nursing with drinking while pregnant. Alcohol goes straight from an expectant mom’s bloodstream through her placenta. A fetus will have the same blood alcohol concentration as her mother. I’m not saying you shouldn’t have a drink while pregnant, but it’s a different calculation.)

Several studies also suggest that lactating women get significantly less drunk than formula-feeding moms and other women do when they all consume the same amount of alcohol. Although it’s unclear why, milk production seems to lower peak blood alcohol concentration, even though nursing moms don’t necessarily feel any less tipsy. (Yay!) More good news: The toxic byproduct of alcohol metabolism, a compound called acetaldehyde, doesn’t pass into breast milk at all.