British doctors are warning that Muslims preparing to undertake the pilgrimage to Mecca should be aware of considerable health risks involved.
An estimated two million visit Mecca to take part in the Hajj each year
More than two million people take part in the pilgrimage to Mecca, known as Hajj, each year.
All able-bodied Muslims who can afford to must perform Hajj at least once in their lifetime.
But, warns the British Medical Journal, risks include sunstroke, heat exhaustion and infectious diseases.
This year some 20,000 British Muslims are expected to take part in the annual Islamic ritual which follows a pilgrimage set out by the Prophet Muhammad.
But doctors in the medical journal warn that the five-day pilgrimage and its rituals, due this year to take place in late January, can prove as physically demanding as it is spiritually challenging.
AVOIDING HAJJ RISKS
Avoid too much sun exposure
Travel by night
Carry a parasol by day
Drink lots of water
Eat salty foods
Wear strong shoes
"In view of the very large numbers of people from disparate regions and the hostile climate of the Arabian desert, the chances of disease, particularly in elderly and infirm people, are high," the journal says.
The biggest dangers, the journal says, are heat stroke and heat exhaustion as the ritual requires the pilgrims to travel long distances in desert conditions.
"It is the most complex of Islamic rituals and involves... walking long distances and camping in desert tents, often with only the most basic sanitation."
The doctors recommend travelling by night and, as men on Hajj are prohibited from covering their heads, to carry a good quality white umbrella during the day to deflect heat.
Travelling by night is recommended as a way to avoid the stampedes that are the most common cause of minor injuries during the Hajj season.
Under Saudi law all pilgrims must be vaccinated against meningococcal meningitis before entering the country.
Doctors advising Muslims ahead of departure are urged to ensure they have been vaccinated against Hepatitis A and B and to prescribe anti-malarial tablets.
It also warns that opportunistic barbers offering to shave male pilgrims' heads, also one of the rites of Hajj, often re-use blades, exposing the pilgrims to blood borne infections like HIV, Hepatitis B and C.