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.

This isn’t to say that drinking and breast-feeding can’t be risky. “It is, of course, important to discern between ‘a few occasional drinks,’ such as having a beer or two or perhaps a glass of wine at dinner, and then ‘binge drinking,’ ” says Maija Haastrup, a clinical pharmacologist at the Odense University Hospital in Denmark, who co-authored the review I previously mentioned. “Another matter entirely is chronic alcohol abuse, which is a problem for a lot of other reasons.” And if you do get tipsy or drunk, you could drop or otherwise accidentally hurt your baby while caring for her. Research suggests you’re three times more likely to have an accidental fall if you’ve been drinking than if you have not. Finally, it’s never a good idea to share a bed with your baby if you’ve been drinking.

There’s also some research suggesting that nursing after drinking can affect your baby’s sleep, but it’s unclear exactly how. In one study, babies fed alcohol-laced milk slept more frequently but for shorter periods each time, whereas in another, babies spent less time in active REM, or rapid eye movement, sleep in the three and a half hours after consuming alcohol-laced milk but made up for these REM deficits later. The differences were small, though—in the latter study, the babies spent eight minutes less in REM sleep, on average, in those first few hours than babies in the control group did. “We are talking about rather subtle changes, and whether or not they have any consequences has not been thoroughly investigated,” Haastrup says.

(As an aside, it’s telling that these studies—which involved giving mothers a drink and then asking them to nurse their babies—passed institutional ethics boards. The ethical standards for the Society for Research in Child Development require that scientists “use no research procedure that may harm the child either physically or psychologically.” Clearly, then, the researchers involved in these studies, as well as their institutions, didn’t think there was a potential risk posed by giving women drinks before having them nurse their babies.)

It is, unfortunately, doubtful that alcohol will boost milk supply, even though we’ve been told for a long time that it does. (At the turn of the 20th century, Anheuser-Busch even marketed a low-alcohol beer called Malt Nutrine to lactating women.) In a 1991 study, researchers gave ethanol mixed with orange juice to nursing moms and found that immediately afterward their babies ate about 20 percent less. It seems that alcohol actually reduces milk release in part by inhibiting the let-down reflex. (These babies didn’t go hungry, though; they made up for this lost milk by eating more frequently later on.) But, you say, what about beer? There is limited evidence that barley, used to make beer, can stimulate the secretion of the hormone prolactin, which is involved in milk production. The big question is how the two opposing forces—the milk-stymieing effects of alcohol and the milk-promoting effects of barley—balance out when a nursing mom imbibes a beer. No studies have tackled this one yet.

There’s one more study worth mentioning, because it is often cited in parenting books and websites as evidence that drinking and breast-feeding is dangerous. In 1989, researchers tested the cognitive and motor development of 400 1-year-olds and then compared their results to the amount of alcohol the babies’ mothers had consumed while breast-feeding. They found that the babies of nursing moms who had consumed at least one alcoholic drink each day did not differ in measures of cognitive development from babies of teetotaling moms, but that they did score lower on tests of motor skills. But here’s the thing: When these same researchers conducted a follow-up study six months later, they were unable to replicate their findings. By 18 months, in other words, the babies of moms who drank while breast-feeding scored the same on motor tests as the babies of moms who abstained.

Bottom line is this: Nursing moms shouldn’t worry about having a few drinks over the holidays. I’m not saying to go out and get blitzed every night between Christmas and New Year’s—as fun as that might sound, it’s risky, and believe me, you do not want to experience a nursing mom’s hangover. Still, rest assured that your baby is not going to end up drunk if you have a few glasses of eggnog before nursing her to sleep.