The Mnemonic is PMs Pet (PETAL) ( The Prime Ministers pet a little cat called Petal)
PETAL stands for Psoriasis, Eczema, Tinea, Annular Erythematosus and L for Lupus, Lichen Planus and Lues an old name for syphilis.
The PM bit stands for Pityriasis rosea, Pityriasis versicolor, Pityriasis alba, Pityriasis rubra pilaris, Pityriasis Lichenoides and Pityriasis rotunda
The M is for mycosis fungoides a type of T cell lymphoma but also the Sezary variant
The small s stands for Solar damage, Scabies, Syphilis and Syndromes
Now we have dealt with the common red scaly conditions already mostly in the mnemonic PETAL and the P of PM If the condition does not seem to fit any of the common red scaly diseases then consider the rarer conditions below.
Small s Solar Lots of red scaly lesions on sun damaged skin here is Australia are solar keratoses or SCC in Situ particularly Bowen's disease. On the lower legs Bowens can look very much like Psoriasis and can have a similar dermatoscopic picture of red dot vessels.
The other condition looking similar is DSAP or disseminated superficial actinic porokeratoses
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| DSAP |
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| DSAP |
Small s Scabies The Crusted variant is particularly scaly and often maximal in acral areas such as the hands and on the ears.
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| Scabies looking like psoriasis |
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| Scabetic burrows |
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| Extensive crusted scabies |
Small s Syphilis is a great masquerader Secondary syphilis gives a red scaly rash on the trunk similar to Pityriasis rosea but it also often involves the hands and feet and has other mucosal features.
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| red scaly areas palms |
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| Relatively non specific red scaly rash trunk |
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| Red scaly secondary syphilis |
Small s Syndromes CIE Congenital ichthosiform keratoderma is the commonest underlying ichthotic disorder in a Collodion baby
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| Child with CIE |
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| Adult presentation |
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| CIE scaling |
Other red scaly syndromes include Refsum, Sjogren Larsson, KID , Netherton ,
You look at an infant or small child with an atopic eczema like rash but not in the usual areas and the child looks funny- abnormal ears or eyes too wide apart or fingers and toes not normal or hair thin and breaks easily or simply no good family history of atopic diseases then you should consider some of the diseases below and decide what blood or urine tests you are going to order.
Syndromic Ichthyoses
These are rare genetic disorders where the skin's barrier function is deeply impaired, causing universal redness and scale production alongside other organ involvement:
- Netherton Syndrome: Classic triad of diffuse, red, scaly skin (ichthyosis linearis circumflexa), structural hair defects known as "bamboo hair" (trichorrhexis invaginata), and severe allergic tendencies like asthma or high IgE levels.
Double edged scale of Nethertons - KID Syndrome (Keratitis, Ichthyosis, and Deafness): Characterized by vascularizing keratitis of the eyes (which can lead to blindness), profound sensorineural hearing loss, and red, thickened, scaly plaques on the skin.
KID syndrome from Dr Shahbaz Janjua 
KID syndrome from Dr Shahbaz Janjua - Refsum Disease: A metabolic syndrome causing scaly skin, progressive vision loss (retinitis pigmentosa), peripheral neuropathy, and ataxia due to the body's inability to break down phytanic acid.
Note the shortened toes in this condition 
- Sjögren-Larsson Syndrome: Features congenital ichthyosis (reddish-brown scales), spastic diplegia or tetraplegia (neurological weakness/stiffness), and intellectual disability.
Sjogren Larsson Sometimes have diabetes as well
Other red scaly eczema like syndromes include See This Reference for these rarer diseases
Several congenital genetic disorders (genodermatoses) can present at birth or during early infancy with widespread red, scaly, and eczematous skin lesions. These rare syndromes frequently mimic severe, treatment-resistant atopic dermatitis but are distinct genetic entities.
Primary Immunodeficiency Syndromes
These rare genetic conditions compromise the immune system, leading to high levels of inflammation and severe eczema-like skin flare-ups.
- Hyper-IgE Syndromes (HIES): Also known as Job's syndrome, it causes a severe newborn eczematous rash alongside recurrent bacterial skin and lung infections.
- Wiskott-Aldrich Syndrome: An X-linked recessive disorder presenting in early infancy with bleeding issues (due to low platelets), immune deficiencies, and severe, widespread eczema.
- Omenn Syndrome: A form of severe combined immunodeficiency (SCID) that manifests shortly after birth with bright red, peeling skin (erythroderma), a seborrheic-like rash, and hair loss.
- IPEX Syndrome: An acronym for Immune Dysregulation, Polyendocrinopathy, Enteropathy, X-linked syndrome. It triggers early-onset autoimmune problems, severe diarrhea, and an intense eczema-like rash.
Congenital Ichthyosis Syndromes
Ichthyoses are hereditary disorders characterized by a defective skin barrier that causes massive accumulation of dry, fish-like scales.
- Netherton Syndrome: Characterized by a triad of generalized red, scaly skin (ichthyosiform erythroderma), distinctively fragile "bamboo" hair, and severe, allergy-driven eczema.
- Congenital Ichthyosiform Erythroderma (CIE): Infants are often born inside a shiny, tight casing called a collodion membrane. Once it sheds, the skin beneath remains persistently red, dry, and covered in fine white scales.
- Peeling Skin Syndrome (Type B): A congenital condition that causes lifelong, continuous shedding and peeling of the skin, accompanied by redness and intense itching.
Metabolic and Nutritional Deficiencies
Inborn errors of metabolism can prevent the absorption or processing of essential nutrients, quickly destroying the skin barrier. [1]
- Acrodermatitis Enteropathica: An inherited defect in zinc absorption that triggers a raw, red, scaly, and blistering rash. The rash concentrates specifically around the mouth, anus, and extremities.
- Biotinidase Deficiency: A metabolic disorder causing a scaly, eczematous rash around the face and eyes, accompanied by hair loss and developmental delay
