Massaging small babies with sunflower seed oil is a cheap and easy way to protect them against infections, doctors advise.
Premature babies are prone to infections
Premature babies are at increased risk of life-threatening infections because their skin is under-developed and lacks full barrier protection.
A study in the Lancet shows anointing the skin with sunflower seed oil helps restore this barrier to cut infections.
The findings are particularly important for developing countries, they say.
Every year over 13 million babies are born prematurely across the world - many in developing countries.
Mortality is particularly high in poorer countries because the babies often require specialist medical treatment which can be expensive, and infection is a major problem.
Dr Gary Darmstadt and colleagues from Johns Hopkins University in the US studied premature babies born in Bangladesh.
Mothers there, as in much of South Asia, massage their babies with mustard oil.
But unlike sunflower seed oil, Dr Darmstadt believes this could be doing more harm than good because it has a toxic rather than a protective effect on the skin and delays recovery of the skin's natural barrier.
He ran a trial where 497 premature (less than 33 weeks gestation) and low birth weight (less than 1.5kg) babies were randomly assigned to receive sunflower seed oil, a petroleum-based ointment called Aquaphor or no intervention.
The treatments were applied to the entire body of the babies, apart from the scalp and face, three times a day for the first 14 days and then two times a day until the babies were discharged from the hospital.
During this time, the researchers looked for signs that the babies had caught any infection.
The babies treated with the sunflower seed oil or the Aquaphor had about seven infections per 100 days in hospital, while the babies who had no intervention had nearly 11 per 100 days in hospital.
When the treatments were started within 24 hours of the baby being born they reduced the risk of infection by up to 60%.
Given that sunflower seed oil is cheaper and more readily available, and performed equally as well if not better than Aquaphor in the study, the researchers said mothers in countries like Bangladesh should be encouraged to use it on their babies.
Dr Darmstadt said: "The challenge now is to discourage use of mustard oil and persuade people to use alternative, proven, available and low-cost products such as sunflower seed oil."
Dr Andrew Lyon, consultant neonatologist at Edinburgh Royal Infirmary, said good handwashing remained the major strategy for reducing infection among newborn babies.
"Application of sunflower seed oil, or indeed anything, will be ineffective if hand hygiene is not good."
He said sunflower seed oil could help cut infections, but only if it was applied correctly which would require some training of staff and parents.
A spokeswoman from the premature baby charity Bliss said: "We know from experience that baby massage holds a number of benefits, both emotional and physical for premature babies.
"It is very positive news."