Paris is not just the political, financial and cultural capital of France, but also the center of a tourist industry that makes up around 8% of the French economy. More than 22 million tourists stayed in Paris hotels in 2014, according to the Visitors Bureau – and if insecurity pushes that number down long-term, effects would be severe.

Anxiety is also showing up beyond France. International airlines and hotel groups such as Delta (DAL), American (AAL), and Hilton (HLT) fell in mid-day trading, as did Asian airlines.

Despite investor worries, the long-term impact of the tragedy on travel and tourism is unclear. The Sept. 11 attacks in the U.S. were a major blow, particularly for the airline industry. But the reaction to subsequent violence has been more muted. In a recent study, Deloitte found that hotel demand fell only marginally because of terror attacks, particularly in comparison to economic factors like the recession. The authors attributed this to “the emergence of a ‘carry on as normal’ culture in response to terrorism.”

But that attitude of considering terrorism as a routine risk like natural disasters may not continue for long. After a decade with only sporadic major terror attacks, the last year has seen a steady drumbeat across Europe, the Middle East, and Africa. It’s not just on political targets like Charlie Hebdo, but also on beach resorts, museums, and, perhaps most notably, passenger airliners.

The circumstances of the Friday attack also have broad implications for European travel. One of the attackers, Ahmad Al Mohammad, is purported to have reached France through Greece as a Syrian refugee, and the U.K.’s Telegraph reported about evidence showing that at least part of the attack was planned in Syria.

With the Syrian refugee crisis spreading and deepening, travelers could draw the conclusion that Europe, overall, is no longer safe. This would have serious consequences: a 2013 CNN survey found travelers were more likely to consider security and safety than any other factor in making travel choices.

The impacts on French tourism, specifically, will become more visible in the coming days. But that may depend as much on official responses as on the more general perception of the attacks. Attractions including the Louvre and the Eiffel Tower have already re-opened, but a broader return to normality could be slow. On Monday, French President François Hollande floated the possibility that a state of emergency may continue for up to three months.

That would entail tighter border controls and more visible internal security, potentially including a stepped-up police and military presence. Those measures could make travelers feel safer—or keep them away by casting a dark pall on the City of Light.

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