Firefighters responded to reports of a chemical incident at a house on Vansittart Road in Forest Gate.
The incident is believed to have been caused by mixing chemicals when cleaning a toilet.
One man and one girl suffered from breathing difficulties and were taken to hospital by London Ambulance Service.
Firefighters ventilated the property.
Two fire engines and two Fire Rescue Units and a specialist hazardous materials officer attended the scene.
The Brigade's 999 Control officers were first called about the incident at 0133, with crews from Leytonstone, Stratford, Bethnal Green and Euston fire stations sent to the scene. The incident was over for firefighters by 0237.
The Brigade’s lead officer for dealing with hazardous materials, Group Commander Matt Hayward, says this is a timely reminder to Londoners to always read the labels and instructions on cleaning products. He said: “The label will always tell you how to safely use the product, and the risks of mixing it with other things. Always follow the instructions on the container to ensure you are using your cleaning products safely. People often think that cleaning products will be twice as effective when mixed, but it can be a recipe for disaster.
“If you do accidentally mix chemicals and start to feel unwell, make sure you leave your property immediately and stay out whilst you call 999 for assistance. We have crews that are trained and equipped to deal with these incidents, so we are ready to help if required.”