It has long been known that new mothers can experience intense sadness, anxiety and stress after giving birth.

But experts say fathers can also develop postnatal depression - although the condition often looks different and is far less likely to be diagnosed. 

Also known as postpartum depression, postnatal depression is thought to affect around one in seven new mothers. 

Symptoms for women, which can develop during pregnancy or within the first year after birth, include low mood, sleep difficulties, poor concentration, guilt and difficulty bonding with the baby.

In more severe cases, thoughts of self-harm or harming the baby are also signs.

The exact cause remains unclear, although changes to hormone levels including oestrogen and progesterone following childbirth, alongside factors such as having a premature or unwell baby, are thought to contribute.

Despite it affecting at least one in 10 men, research into how the condition affects fathers has been far less frequent.

But following a major study earlier this year, experts say there should be renewed attention to how the condition affects fathers. 

They claim that while male postnatal depression is also triggered by hormone changes, the symptoms may be different.

Brett A. Biller, a psychologist at Hackensack University Medical Center, said: 'The perinatal period is a time of significant change for new fathers. 

'They often experience hormonal shifts, including decreased testosterone and increased [oestrogen] and cortisol, which are evolutionary mechanisms to increase attachment to their offspring, but also make them more susceptible to depression and anxiety.' 

Lower levels of testosterone - the primary male sex hormone - have been linked to depression in some studies, while cortisol is the body's primary stress hormone.  

Experts estimate that a father's risk of postpartum depression can rise to around 50 per cent if his partner is also affected. 

Yet only around one in 10 cases are believed to be formally diagnosed, raising concerns that many fathers are quietly suffering. 

A major Swedish study, published in JAMA Network Open earlier this year, analysed more than one million fathers and found diagnoses of depression and stress-related disorders rose by around 30 per cent towards the end of the first year after childbirth, compared with before pregnancy. 

The researchers said that the pressures of fatherhood may be taking a toll over time, and that there may be a potentially problematic gap in postnatal support for men.

They wrote: 'These findings suggest that fatherhood may be associated with a temporary reduction in psychiatric disorder diagnoses followed by increased vulnerability later post partum, highlighting the need for sustained paternal mental health surveillance, particularly for depression and stress-related disorders.'

Speaking to medical website NewsMedicalLifeSciences, Biller said reduced sleep, financial pressures and changes in the relationship with a partner can all contribute to fathers' declining mental health.

Unlike mothers, whose symptoms often centre on sadness and withdrawal, fathers may be more likely to be irritable, angry, aggressive or turn to alcohol and drugs.

Experts warn this can strain family relationships and may increase the risk of emotional and behavioural problems in children. 

The Swedish study suggested that many fathers are also thought to avoid seeking help because they do not want to take attention away from their partner.

Researchers also suggested underdiagnosis may be a factor rather than fewer symptoms. 

They wrote that 'some fathers may minimize or internalize their own mental health symptoms or decrease help-seeking during their partner's pregnancy to avoid diverting attention away from maternal needs.' 

Other signs of postpartum depression for men include social withdrawal, frequent headaches or stomach aches and losing interest in activities they once enjoyed. 

Biller added: 'We can only wonder how pervasive paternal depression and anxiety likely are but are not recognized due to fathers being more reluctant - or unaware of how to report and seek services to address their emotional symptoms.'

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