Image caption Several US organisations ban beards, including the military and police forces

A rabbi is suing the US Army for refusing to let him serve unless he removes his beard. The US military, as well as many police forces across America, require recruits to be clean shaven. But what is wrong with sporting a beard in the line of duty?

Chin straps, goatees, stubble, soul patches, mutton chops or just the old-fashioned full version.

There are many ways to grow a beard, but if you're serving in the US military, getting creative with your chin furniture is not an option.

The different branches of the US insist that recruits are clean shaven. Those later in their career are permitted to go as far as growing a moustache. But even that facial freedom comes with caveats.

"Moustaches are allowed, but hair may not extend beyond the edges of the lips, nor may it extend below the top of the upper lip," says a US Army spokesman.

Image caption Rabbi Stern believes he should be allowed to serve with his beard

"Sideburns may not grow below a level even with the bottom of the ear canal."

As for beards, well, they're banned.

Serving members of the US Army, Navy and Marine Corps may qualify for a "shaving waiver" if they suffer from medical conditions that make shaving difficult or painful, but still have to keep any facial hair short.

The beard ban has meant some Muslims, Sikhs and Hasidic Jews have been unable to sign up for duty.

"I was told my application to join the army would only be accepted if I shaved off my beard," says Menachem Stern, an Orthodox Jewish rabbi, from the Chabad Lubavitch Community, who applied to join the army as a chaplain in 2008.

The 29-year-old is suing the US Army for refusing him the right to keep his beard, on the grounds of his religious beliefs.

"This is a tenet of our faith - it's not optional not to have one in our community.

"Could you imagine any of the great sages - whether Abraham, Isaac or Jacob - clean shaven?" he says.

Rabbi Stern's case has been taken up by New York Senator Kirsten Gillibrand who has written to the army secretary asking for the beard policy to be modified for chaplains.

In recent years, shaving waivers have been issued for some applicants, and not for others. According to Mr Stern's lawyer, Nathan Lewin, three Sikhs have been given permission to keep their beards since 2009.

LAPD Facial hair regulations Employees shall be clean shaven when reporting for duty. Beards shall be permitted only when required by the nature of the assignment or for a bona fide medical condition

The employee's beard shall be neatly trimmed and not longer than one-quarter inch in length

Male employees may wear a short and neatly trimmed moustache of natural colour

Moustaches shall not extend below the vermillion of the upper lip or below the corners of the mouth and may not extend to the side more than one‑half inch beyond the corners of the mouth

Back in 1976 Mr Lewin fought a case on behalf of a bearded rabbi who wanted to serve in the US Air Force, and won. He's disappointed to be having the same battle all over again.

"I would like to be able to say that government agencies are becoming more accepting of various aspects of appearance but frankly Rabbi Stern's experience with the US Army leads me to conclude that there are still very strong restrictions that the people who have control over these institutions are imposing."

'Group identity'

But why is there a ban in the first place?

A US Army spokesman said it was to do with "long-standing traditions of uniformity, hygiene, and good order and discipline", adding that it was in keeping with strict dress codes which required a sense of professionalism and group identity.

Beards are also banned in the US military for practical reasons, explains Penny Jolly, a professor of art and art history, who has studied social trends in appearance.

"They were eliminated in the US military in WWI due to the need to wear gas masks. Razors were issued in GI kits, so men could shave themselves on the battlefield," she says.

The gas mask argument is also often made by police forces - though across the US a patchwork of different rules and regulations exists.

'Excessively bushy'

At the end of last year, Durango County police force in Colorado relaxed its rule to allow officers to sport goatee beards (which apparently do not affect the seal between the gas mask and the face).

In the opposite direction of growth, New York's police department tightened its follicular restrictions in 2008, banning goatees, chin straps and "designer beards".

Moustaches are generally permitted in the police, but subject to some strict rules.

The Chicago police department reportedly outlaws moustaches that are "excessively bushy, rolled or curled".

Los Angeles Police Department, one of the largest police forces in the country, says they must be neat and tidy and of a natural colour.

"Moustaches shall not extend below the vermillion of the upper lip or below the corners of the mouth and may not extend to the side more than one half inch beyond the corners of the mouth," reads the LAPD moustache manifesto.

Handlebar moustaches

The British armed forces also have a troubled relationship with facial hair.

Image caption Some operatives in Afghanistan sport beards to help them win the trust of the local population

In the Army and RAF, beards are generally allowed only on medical or religious grounds, though some infantry regiments have a rank of "pioneer sergeant" - responsible for carpentry and joinery - which comes with the right to grow a beard.

The British Navy also has its own beard tradition - allowing a "full set" (beard plus moustache) on the permission of the commanding officer. The Navy does not accept the argument that a beard prevents a gas mask working effectively.

The RAF, for its part, has a fondness for handlebar moustaches - far bushier than anything allowed in the US forces. One British airman with floral facial hair got into hot water when temporarily attached to the USAF.

But while joining the army can sometimes be difficult for Muslims, Sikhs and Jews who feel obliged by their faith to grow a full beard, in a country like Afghanistan, the boot is on the other foot. Here it's the US and British servicemen who have a challenge fitting in.

"Our men in the field are growing their beards because the Afghan soldiers think it is respectful," said a Ministry of Defence spokesman in 2006. "For men working very closely alongside the Afghans for long periods, wearing beards has proved to be an excellent way of helping to win trust and breed understanding."

US special operations units in Afghanistan have also long worn beards to gain the respect of tribal elders. Combined with wrap-around sunglasses, though, the look is sometimes more Hell's Angel than Helmand.