What combination feeding is

The NHS calls it "mixed or combination feeding": giving your baby both breast milk and formula, or breast milk from the breast and from a bottle. People do it for many reasons — returning to work, sharing feeds with a partner, topping up on medical advice, building supply back up after a difficult start, or simply wanting to.

The HSE lists the same range and adds relactation — starting breastfeeding after bottle feeding — and low milk supply. None of these needs justifying. What does need understanding is how supply responds.

How it affects your milk supply

The NHS states it directly: "Introducing formula feeds can affect the amount of breast milk you produce." The HSE explains the mechanism: "The more you breastfeed or express (remove) your breast milk, the more milk you'll produce. If you begin giving formula to your baby while you are breastfeeding, they'll take less of your breast milk. This means your body will produce less milk."

This is not a warning against combination feeding. It is the information you need in order to do it on purpose rather than by accident. Each formula feed that replaces a breastfeed removes a production signal, and supply adjusts downwards over days to weeks. If you want to keep a particular level of breastfeeding, you have to decide which feeds you are protecting.

The HSE also advises, where possible, breastfeeding for the first weeks before introducing bottles, because the early weeks are when supply is established.

Introduce it gradually

The NHS is specific about why: do it gradually "to give your body time to reduce the amount of milk it makes — this helps lower your chance of getting uncomfortable, swollen breasts, or mastitis". If you are returning to work, starting a few weeks beforehand gives both of you time to adjust.

In practice:

Replace one breastfeed at a time.
Wait several days before replacing another, so your breasts can adjust.
If your breasts become uncomfortably full, hand express just enough for comfort — not to drain.
Keep the feeds you most want to protect. Early morning feeds tend to be the largest.

The HSE flags the engorgement risk plainly: when your baby takes less from the breast, your breasts can become too full, and if that happens it is important to remove some milk by hand or by feeding.

Giving the first bottle

Both the NHS and HSE give the same practical advice, which exists because breastfed babies often refuse the first few bottles:

Offer it when your baby is happy and relaxed, not very hungry.
Have someone else give the first bottles, so your baby is not near you and smelling your milk.
Use a slow-flow teat to mimic the flow of breastfeeding (HSE).
Use similar positions to breastfeeding, and hold your baby fairly upright.
Pace the feed: let your baby pause, and follow their cues rather than emptying the bottle.
Express regularly between bottle feeds to help maintain supply (HSE).

The NHS notes there is evidence that some babies find it harder to breastfeed after learning a different sucking technique. This is not universal and it is not a reason to avoid bottles — but it is a reason to get breastfeeding established first where you can, and to keep bottles paced and responsive.

What to expect

The HSE sets realistic expectations:

It may take time for you and your baby to adjust.
Giving a bottle at night does not mean your baby will sleep through — they may still want the comfort of breastfeeding.
Some babies become more windy or constipated when formula is introduced.

It also warns about a specific trap: some parents think they have low supply, add formula as a result, and end up overfeeding. Breastfeeds and bottle feeds both count towards the milk your baby needs — a bottle is not an addition to a full day's breastfeeding.

Going the other way: increasing breastfeeding

If you want to shift the balance back towards the breast, the NHS lists what helps: plenty of skin-to-skin contact, expressing regularly (around eight times a day), feeding responsively whenever your baby shows hunger cues, and gradually reducing bottle feeds as your supply increases. The HSE says the same about combination feeding — gradually offer less formula, and you are likely to produce more milk as demand at the breast rises.

Do this with your baby's weight being monitored, and with support. UNICEF UK's Baby Friendly Initiative publishes specific guidance on maximising breastmilk and relactation, and an IBCLC or breastfeeding counsellor can build a stepwise plan.

Practical points on formula and expressed milk

Make up formula feeds fresh, following the manufacturer's instructions and your national guidance on water temperature and preparation. Store expressed breast milk according to NHS or HSE guidance and label it with the date. Do not mix leftover formula and expressed milk in a way that means you have to discard breast milk you have worked for.

When to get help

Contact your midwife, health visitor, public health nurse or lactation specialist if:

Your baby is not gaining weight, or is having fewer wet and dirty nappies than expected.
You think you are not producing enough breast milk (HSE) — ask for a feeding assessment before adding routine top-ups.
You develop sore nipples, engorgement or mastitis while introducing bottles.
Your baby was premature or spent time in hospital and is transitioning to breastfeeding.
You are having medical treatment or spending time away from your baby and need a plan.

Combination feeding is a legitimate choice, not a failure of breastfeeding. The goal is to make it a decision you have made deliberately, with your supply behaving the way you intended.

Where to get real help

Most breastfeeding problems are solved faster by someone watching a feed than by reading about them. In the UK the National Breastfeeding Helpline is 0300 100 0212 and, as its operators the Breastfeeding Network and the Association of Breastfeeding Mothers state, it is open "24 hours a day, 365 days a year", with support also available in Welsh, Polish, Bengali and Sylheti (nationalbreastfeedinghelpline.org.uk). La Leche League GB runs local groups and a helpline; in Ireland the HSE offers an "Ask our breastfeeding expert" live chat and email service. An IBCLC is an International Board Certified Lactation Consultant, the only internationally accredited lactation qualification — you can check credentials through IBLCE. Your midwife, health visitor or public health nurse can also refer you.

Combination Feeding: Breast and Formula Together