Starting Combination Feeding: What You Need to Know About Sterilising
Combination feeding – mixing breastfeeding with bottle feeds – is far more common than people realise. Whether you're introducing formula top-ups, expressing milk into bottles, or gradually shifting the balance as you head back to work, one thing changes immediately: you need to sterilise.
Here's a straightforward guide to sterilising when you're combination feeding, without the faff.
Why sterilising matters when you start combination feeding
When you breastfeed directly, your milk is delivered at body temperature and consumed immediately – there's no equipment involved that bacteria can colonise. The moment you introduce bottles, that changes.
Bottles, teats, rings, and lids all have surfaces where milk residue can build up and bacteria can multiply, even after what looks like a thorough wash. For newborns and young babies whose immune systems are still developing, that's a genuine risk – which is why the NHS recommends sterilising all feeding equipment until your baby is at least 12 months old.
This applies whether the bottle contains formula, expressed breast milk, or a combination of both.
How often do you need to sterilise when combination feeding?
Every time, before every feed. That means after washing the bottle with hot soapy water or in a dishwasher, you sterilise before it gets used again – not just once a day.
When you're combination feeding, the volume of equipment you're running through can quickly double or triple compared to exclusive breastfeeding. A typical combination feeding day might mean 3-5 bottle feeds alongside breastfeeds, each requiring a washed and sterilised bottle.
For many parents, this is where the combination feeding routine starts to feel unsustainable – not the feeds themselves, but the relentless washing and sterilising cycle around them.
Sterilising methods compared
Steam Sterilising
Electric steam sterilisers are the most popular method in the UK. They're fast (around 6-12 minutes), effective, and don't require chemicals. The downside is that you still have to wash bottles thoroughly first, and you need to let them cool and dry separately unless your steriliser has a drying function.
Microwave sterilising
Microwave steriliser bags and units work well and are relatively cheap. The catch is they only hold a limited number of bottles at once – usually 4 – and you need to be present for the whole cycle. Not ideal when you're also feeding a baby.
Cold water sterilising
Milton tablets and similar products sterilise without heat. Bottles need to be fully submerged for at least 15 minutes, and some parents notice a faint chemical taste. Fine as a backup method; less practical as your main approach.
All-in-one bottle washers
A 4-in-1 unit like the Bebello washes, rinses, sterilises, and dries in a single automated cycle. You load the bottles, press start, and come back to clean, dry, sterilised bottles ready to use. For parents combination feeding and running 4-6 bottles a day through the cycle, it's the option that removes the routine entirely rather than just streamlining it.
How to store sterilised bottles between feeds
Once sterilised, bottles stay sterile for up to 24 hours if kept sealed or assembled with a teat and lid in place. After that, sterilise again before use. Bebello Washer allows bottles to maintain sterility for 72 hours due to the controlled HEPA-filtered environment.
Don't leave sterilised bottles on a drying rack or open on a surface – that reintroduces bacteria within hours. If your steriliser has a sealed storage function, use it. Otherwise, assemble the bottles immediately after sterilising and store in the fridge.
A note on paced bottle feeding
If you're combination feeding and want to protect your breastfeeding supply, paced bottle feeding is worth knowing about. It involves holding the bottle horizontally, letting your baby control the flow, and taking regular breaks – mimicking the pace of breastfeeding.
This helps avoid breast refusal, which is the most common concern when introducing bottles alongside breastfeeding. Your midwife or health visitor can show you the technique, or there are good NHS resources online.
If you're combination feeding and finding the washing and sterilising cycle relentless, the Bebello 4-in-1 bottle washer automates the whole process: wash, sterilise, and dry in one cycle while you get on with feeding. Worth a look.
Frequently asked questions
Do I need to sterilise bottles if I'm only putting breast milk in them?
Yes. The bottle itself – not what goes in it – is what needs sterilising. Bacteria can grow on milk residue regardless of whether it's breast milk or formula.
How long does sterilised equipment stay sterile?
Up to 24 hours if kept sealed and assembled. In practice, it's easiest to sterilise just before each feed or batch sterilise at the start of the day and keep bottles sealed until needed.
Can I sterilise in a dishwasher?
A dishwasher cleans but doesn't sterilise at the temperatures used in a domestic cycle. You still need to sterilise after washing, using steam, microwave, or cold water method.
When can I stop sterilising?
The NHS recommends sterilising feeding equipment until your baby is 12 months old.