A cot death charity has raised doubts over the benefits of Finnish-style baby boxes, which infants can sleep in.
Issuing new advice to parents, The Lullaby Trust said there was no evidence baby boxes reduced the rate of sudden infant death syndrome (SIDS).
The cardboard box, filled with baby products and a mattress, can itself be used as a bed, and has been given to new parents by some NHS trusts.
The charity said its leaflets would no longer be put in the boxes.
"We will no longer allow our branded leaflets to be enclosed...as this suggests we endorse the product," said the charity, which provides expert advice on safer baby sleep for the NHS.
The box tradition originates from Finland, where for 75 years, every pregnant woman has been given a box filled with things like nappies, clothes, bedding and a mattress.
Finland has one of the lowest infant mortality rates in the world - two deaths per 1,000 live births, compared with a global rate of 32 in 1,000, according to the UN.
Francine Bates, chief executive of the Lullaby Trust, told BBC Radio 5 live Finland's "fantastic record" was due to a variety of reasons, including lower teenage pregnancy rates.
She said: "The fact that they give a box out to every family may be a factor but we can't say that definitively."
'We were reluctant to give it up'
Miia, 40, and her partner Tim, from Reading, were sent a baby box by her Finnish mother when their son was born eight months ago.
She told the BBC: "It's quite a traditional thing. I slept in one myself. You get a box full of baby clothes from newborn to one years old.
"The idea is that you get the basics so you don't have to buy any more. You also get toys and toothbrushes and all sorts of other things.
"A foam mattress is included so you can use it as a box to sleep in. We ended up using it until he was about five months old.
"We kept the box on the floor next to the bed on my side. He was happy and I think he felt quite safe in it. I was quite reluctant to move him away from it.
"But when he got bigger he started to wake himself up knocking against the side of the box. It was getting a bit snug."
A box scheme is due to be rolled out for all newborn babies across Scotland this month. Some areas in England also give out boxes.
A spokesperson for the Scottish government said it was "proud" to introduce the box in Scotland, where it will "help tackle deprivation, improve health and support parents".
They said the Scottish baby box meets the "highest safety standards", adding: "It was awarded British Safety Standard accreditation as a crib for domestic use - the first non-commercial baby box in the world to do so."
Ms Bates said that while the boxes can be tested for elements of safety standards, "the fact is there is no safety standard anywhere in the world that applies directly to a cardboard box".
"We're very clear that a cot or a Moses basket is the safest place for a baby to sleep," she said, adding that she was concerned the boxes were being marketed as products to reduce sudden infant death syndrome.
However, she said the box may be a good option for daytime naps if there is no alternative, and that it was "certainly a better alternative than sleeping a baby on a beanbag or a sofa".
SIDS, also known as cot death, is the sudden unexplained death of an apparently healthy baby.
There were 230 sudden infant deaths in the UK in 2014, following a downward trend in the last decade. In 2001, there were 330.
The do's and don'ts of baby boxes:
If you do decide to use a baby box, the Lullaby Trust recommends the following:
- Only use the box for daytime naps and sleep your baby in a cot or a Moses basket next to your bed during the night
- Do not use the box once your baby is able to roll
- Do not put extra bedding on top of the mattress to raise your baby up to a higher level
- Make sure the box is placed on a solid surface and cannot topple over
- Do not use the box if it gets wet or soiled
- Do not put the box on an under heated floor
- Keep pets away from the box
- Do not leave the baby unattended or out of view
- Do not lift or carry the box around your home if the baby is in it
- Do not put the lid on the box if your baby is in it
- Make sure you comply with any instructions relating to maximum age and weight