Richard Forman and Jianguo Wu suggest that sustainable city expansion should be restricted to selected urban peripheries (Nature 537, 608–611; 2016). Our investigations across five Indian cities indicate that proper planning of such peri-urban areas is crucial.

We define peri-urban areas as a 5-kilometre fringe of development beyond a city's jurisdiction. The India Research Initiative for Peri-Urban Human–Animal–Environment Interface, funded by Canada's International Development Research Centre, is examining the effects of expansion around Bangalore, Ludhiana, Guwahati, Bhubaneshwar and Udaipur on city dwellers. The populations and calculated decadal growth rates of these cities vary from 8.44 million and 49% (Bangalore) to 0.45 million and 14% (Udaipur).

Our findings indicate that poor farming practices across all of these peri-urban areas could put food safety at risk, promote the spread of tuberculosis and other zoonotic infections, and accelerate microbial resistance through antibiotic overuse in livestock (our unpublished results). Public health is further threatened by minimal access to proper health care and by inadequate waste-management systems.

Without strict oversight, sound planning and investment in building infrastructure, peri-urban belts stand to aggravate many of the adverse effects of rapid urban growth.