It seems that van Rysselberghe really liked Pointillism and the related Divisionism a lot, never totally abandoning (while watering down) the concepts later in his career when many of his paintings were more conventional.
But he had to earn a living and, as for many painters, that required making portraits. So van Rysselberghe often tried to include as much Pointillism as he could in a number of those portraits. The problem is, Pointillism and portraiture do not mix easily. That's because Pointillism in its pure form cannot handle small details and sharp edges, things that portraits traditionally require.
So compromises usually had to be made, as the images below indicate. They are presented in roughly chronological order.
An early Pointillist portrait.
This features many little colored dots on the subject's face, but van Rysselberghe had to use some conventional brushwork on the ear, the lower part of the nose and upper lip, and the eyes.
A mix of hard edges and dots here.
Pointillism doesn't always work for hair, either.
By the time he did this portrait, Rysselberghe was resorting to conventional painting for faces and hands.
Around 1900, he was using plenty of sharp lines, leaving Pointillism for flat, plain surfaces.
Closer view of how he was treating faces.
From the same era: a selective mix of forms and dots.
Since this wasn't a commissioned portrait, Rysselberghe could enjoy using much pointillism here, though some lines are strategically used.
An example of his brushwork in a more Divisionism mode, though key facial features are drawn, not dabbed.
Pointillism and Divisionism can be seen here, but they are incidental to the depiction.
This portrait has bright colors, but otherwise is almost conventional.
Another near-conventional work, but the coloration gives it an Impressionist feeling even though sharp details are present.