Millions of children around the world are marking the United Nations' first Global Handwashing Day.
In India, cricket star Sachin Tendulkar will be leading the campaign that will see children across South Asia simultaneously washing their hands.
The UN says it wants to get over the message that this simple routine is one of the most effective ways of preventing killer diseases.
Nearly half the world's population do not have access to adequate sanitation.
'Critical times'
More than 120 million children in 70 countries across five continents are expected to participate in the campaign.
From Kabul to Karachi and from Delhi to Dhaka, millions of children will take part in the campaign and pledge to embrace more hygienic practices by the simple act of washing their hands.
India has recruited one of the country's biggest sporting icons, cricket star Sachin Tendulkar, to be the face of the campaign.
Washing hands will be the topic of Afghan television and radio talk shows and Pakistani newscasts.
Nepal's new Maoist government is sending out mobile text messages. In Bhutan, special animated videos have been made with Bhutanese characters.
"The message we are really trying to get out is the importance of correctly washing your hands with soap and water at the critical times," Unicef's senior Sanitation and Hygiene programme adviser, Therese Dooley, said.
"And those critical times are before you cook or prepare food, before you eat and after using the toilet and after cleaning a baby."
The UN says washing hands with water alone is not enough "because you fail to wash off the germs".
"We are recommending hand-washing with soap," Ms Dooley said.
Unicef says using soap to wash hands, particularly after contact with excreta, can reduce diarrhoeal diseases by over 40% and respiratory infections by 30%.
Diarrhoea and respiratory infections are the main cause for child deaths in India.
Nearly half the population of South Asia has no access to toilets, whilst in sub-Saharan Africa this figure is as low as 28%.
With such poor sanitation standards, it is little surprise that children in the region are susceptible to diarrhoea, hepatitis and pneumonia - often leading to their deaths, the UN says.
The UN is celebrating 2008 as the International Year of Sanitation.
