The main idea is that some skin conditions are contraindications to standard facial treatments because manipulating the skin can worsen the problem. Acne excoriée involves self-inflicted picking, leaving open, inflamed, and fragile skin. Any facial manipulation, extractions, or aggressive treatments can aggravate the lesions, increase inflammation, raise the risk of infection, and cause further scarring. Because the skin is already damaged and sensitive, avoidance of typical treatments is the safest approach until a medical professional has assessed and the condition stabilizes. Milias and whiteheads are common and usually managed with gentle, targeted care; acne without excoriation can often be treated with appropriate precautions. So the condition that may require avoiding treatment is acne excoriée.

Cyanobacteria are photosynthetic bacteria that many people call blue-green algae because they commonly appear in natural water bodies, sometimes forming visible blooms. They’re associated with nutrients like B vitamins, calcium, and protein, which is why this option fits the description. The other algae types—green, brown, and red—are true algae (eukaryotic organisms) with different pigments and cellular structures, and they are not cyanobacteria, so they don’t match the clue about being cyanobacteria in natural waters.

Crust is the dried mass that forms on the skin after an oozing sore heals. It can contain dried blood, serum, pus, epithelial debris, and sometimes bacterial debris. That drying and layering during the healing process makes it a secondary lesion. A vesicle is a small blister filled with clear fluid, not a dried residue. A pustule is a raised spot filled with pus, typically moist rather than dried. An ulcer is a deeper break in the skin with tissue loss, not a dried surface. So the dried, crust-like mass fits the description precisely.

A poultice is a soft, moist paste created by crushing herbs and mixing them with hot liquid, then applying the mass to the skin. The heat and moisture help release herbal constituents and promote their absorption into the tissue. This makes the paste-like preparation intended for topical use. It’s different from an infusion, which is just a liquid made by steeping plants (not a spreadable paste); from a dried herb collection, which is simply the plant material without forming a paste; and from distilling essential oils, which is a process to extract volatile oils, not a topical paste.