He considered photos of them wearing their wigs, or trying on several wigs. Finally, he asked a woman if she would be willing to remove her wig entirely.
It was a crucial moment, he said. It was an unusual request, but she did it.
The Berlin-based photographer can't say exactly what happened -- maybe it was the clarity with which he could see her eyes and face -- but the images were captivating. From then on, he asked all of the women featured in his portrait series, "Unfading," to remove their wigs and reveal bald heads or patchy scalps or smooth foreheads with no eyebrows.
"I was really happy for people to trust me to do this," said Soeder, who photographed the women last year in the United Kingdom. "They were showing an identity that is completely invisible to other people."
More than 6.6 million people in the United States and 147 million people worldwide have or will develop alopecia areata, according to the National Alopecia Areata Foundation. For some, hair falls out in clumps, then grows back, only to fall out again. Others lose hair from their head, eyelashes and eyebrows. People with alopecia are often mistaken for cancer patients, but the condition isn't life-threatening and many people with alopecia are healthy otherwise.
Still, its effects can be isolating and emotionally painful. Soeder photographed a dozen women, ranging from their 20s to their 60s, and one said she had never before met another person with the condition.
Alopecia "really seems like a threat to their sense of identity," Soeder said. "After (hair loss), it's the process of overcoming that. It goes at different speeds for everyone."
Hair loss can be especially difficult for women, Soeder said, and many tried to hide it. He met the subjects for his series through the organization Alopecia UK, and some had tattooed eyebrows and collections of wigs and scarves. A couple said they never took their wigs off in front of others.
In Soeder's portraits, the women stand wig-free, with polished makeup and bright, solid-colored backgrounds.
"Even though it's very uniform and repetitive, in a way ... it really emphasizes people's individuality," he said. "It just increases their uniqueness."
The women were instantly able to see their images on Soeder's computer. He worried it would make them self-conscious. Instead, it seemed to empower them.
"It made people feel confident," he said. "The whole photography process is transparent. There's nothing that happens in between. I think that made the process easier and more interesting, because it was a dialogue."
He hopes this project will reveal to everyone how important it is to accept who you are. One woman told Soeder that before she removed her wig and posed, she'd never before had a beautiful photo of herself.
For many of the subjects, "an inner strength is revealed which is both astounding and beautiful," said Gwennan Thomas, a volunteer with Alopecia UK who's No. 5 in the gallery above. "When faced with adversity, one can make a choice. You decide on the path you take."