Thiomersal is used in preservation of the medicinal products.

Thiomersal belongs to the class of medications called as preservatives. It is used in minuscule quantity in some vaccines (e.g. tetanus and pertussis (DTP), diphtheria and tetanus toxoids (DT)) and works by preventing bacterial and fungal growth.

Irritation of ear, Allergic skin rash

• Seek immediate medical attention in case of any severe allergic reactions. 
• Tell your doctor if you are or planning to become pregnant or are breastfeeding.
• Do not take if you are allergic to thiomersal or any of its ingredients.

Ques. Q. Is thimerosal safe and still used in vaccines?
Yes, thiomersal contains ethyl mercury and is considered safe with no studies indicating it as harmful. It is used in few multi-dose vaccines.