This means it will attack your skin. Wear protective gloves and glasses. The dust, either from mixing or sanding dry concrete, is toxic. Always wet sand rather than dry sand whenever possible. So use preventive measures to make sure you do not develop the sensitivity in the first place.
Allergic dermatitis can also occur due to chromium contaminants in the cement.
The silica in the cement is also highly toxic by inhalation. These sealers are often solvent-based, and need a lot of ventilation when applying. Read the label carefully. Wear gloves, protect your eyes. Read the labels and the Material Safety Data that come with whatever product or additive you are using.