Currency risks can cause you losses becasue surrency markets have high volatility. For example, you will have to pay 5,000 Euros next month. The current exchange rate is 1$:2Euro. That means, you have to pay 2,500$. But when the day of the payment comes, the exchange rate becomes 1$:1Euro. That means you have to pay 5,000$. Instead of paying 2,500, you paid 5,000$. The chance of having a loss due to the varying exchange rate is the currency risk.