Sally Davies said up to 500 people who had visited The Mill pub and the Zizzi restaurant in Salisbury, southwest England, needed to wash their clothes and belongings as a precaution.
The March 4 attack on former double agent Sergei Skripal and his daughter Yulia is being treated by detectives as attempted murder.
The pair were found slumped on a bench in Salisbury. They remain in a critical but stable condition in hospital.
"There has been some trace contamination by the nerve agent in both The Mill pub and Zizzi restaurant in Salisbury," Davies said.
"I am confident this has not harmed the health of anyone who was in The Mill pub or Zizzi's.
"However, some people are concerned long-term exposure to these substances may, over weeks and particularly months, give rise to health problems.
"I am therefore advising... the people who were in either the restaurant or the pub at 1:30pm last Sunday until evening closing on Monday should clean the clothes they wore and the possessions they handled while there."
Pub and restaurant-goers were told to wash their clothing in the washing machine, while dry clean-only clothes should be put inside two tied plastic bags and safely stored while awaiting further advice.
Mobile phones, handbags and electronic items should be wiped with sanitary wipes, which should then be disposed of in domestic waste.
Items such as jewellery and spectacles should be hand-washed in warm water and detergent, before being rinsed in cold water.
The risk to public health remained low and the advice was precautionary, Public Health England said.
"It is possible, but unlikely, that any of the substance which has come into contact with clothing or belongings could still be present in minute amounts and therefore contaminate your skin," PHE said in a statement.
"Over time, repeated skin contact with contaminated items may pose a small risk to health."
Home Secretary Amber Rudd, Britain's interior minister, said Saturday that police were examining more than 200 pieces of evidence, had identified more than 240 witnesses, and were ploughing through security camera footage.
Around 180 troops, including chemical warfare experts, have been deployed in Salisbury after investigators requested specialist assistance.
Skripal, 66, came to Britain in 2010 as part of a spy swap. He was a former colonel in Russia's military intelligence who was jailed in his country for betraying agents to Britain's MI6 secret service.
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