Hamburg - Buds are sprouting, birds are twittering and the convertibles and sunglasses are coming out.

Even though the overnight temperature still drops to near freezing, the flirting season is on. Everyone knows that even the most tender ray of sunshine warms not only the cheeks, but also stirs emotions. Winter coats are aired and scarves loosened as the spirit of spring takes off.

Are all these feelings just a fluke? No, not at all. Although scientists are not in agreement about what causes them, the symptoms are the same: good humour and a tingling in the belly.

"Sunlight and the additional daylight cause an increase in the hormone serotonin and that makes people generally more alert and livelier," said Peter Walschburger, a psychologist at Berlin's Free University. The body also produces less of the sleep hormone melatonin when there is more light. Spirits are lifted and there's an increase in the desire to flirt and have sex. But that's not all by a long shot.

"There are physiological, chronobiological and psychological reasons for the scientifically undisputed 'spring feeling,'" said Walschburger. Above all, spring makes psychological aspects flourish in us. "Conditions for stimulation are simply better than in winter," he said. Women start wearing shorter skirts and deeper necklines. That creates emotional appeal.

"Springtime simply offers more possibilities," said Nina Deissler, who should know. For years she has been organizing flirt seminars in Hamburg.

"The most common times for the desire to have a relationship are always Christmas and springtime," Deissler said. The chances often are better in the spring for very practical reasons. "You shouldn't forget that you tighten your body again when you don't have to put on a winter coat to protect from the ice-cold wind." You can start looking forward again and spot potential flirt partners for the first time.

Professor Horst Harald Klein of the University of Bochum attributes the frequently evoked spring feeling to psychological factors.

"In the end it is not about illness, therefore there's been hardly any scientific investigations into it," he said, adding that he also considers the increased hormone levels an unworthy idea.

"Whether we feel happy or lustful undoubtedly is dependent on a complex puzzle in which psychological factors, sensory stimuli and individual predisposition play a role - not just hormone levels," said Klein, referring to the many optical stimuli people are exposed to in springtime thanks to lighter clothing and friendlier faces.

In fact longer days combined with high spirits don't always unleash good feelings in everyone. Instead of having a tingly feeling in their belly, they feel a leaden tiredness in springtime.

"Also this situation presumably has to do with many different factors," said Klien. In springtime, activity increases and there are more demands on the body. Many people also stay up later. "If someone is tired at 8 o'clock in the evening in spring and it is still daylight outside, it's more obvious than in winter."

This is a very normal adjustment that the body has to come to terms with. Walschburger added that the weather must serve for many things no matter if a person is feeling elation or drowsiness. (dpa)