Inclusion Criteria:

• For subjects with guttate psoriasis:
• * Ability to provide written informed consent and comply with the protocol.
• * At least 18 years of age.
• * Diagnosis of guttate psoriasis.
• * Onset of guttate psoriasis within 12 months.
• * Body surface area (BSA) involvement greater than or equal to 5%.
• * PASI greater than or equal to 4.
• * Subject is considered a candidate for phototherapy or systemic therapy.
• * Subject is unlikely to conceive due to male, post-menopausal, or using adequate contraceptive (barrier, hormonal, implant, or permanent sterilization methods). Women of childbearing potential will be allowed to enroll provided they practice adequate forms of birth control.
• * Physical exam with no evidence of active skin infection and/or other findings that indicate chronic disease or concomitant inflammatory/immune-mediated skin disease other than psoriasis.
• For subjects with chronic plaque psoriasis (control):
• * Ability to provide written informed consent and comply with the protocol.
• * At least 18 years of age.
• * Diagnosis of plaque psoriasis.
• * Duration of plaque psoriasis \>5 years.
• * Body surface area (BSA) involvement greater than or equal to 5%.
• * Subject is considered a candidate for phototherapy or systemic therapy.
• * Subject is unlikely to conceive due to male, post-menopausal, or using adequate contraceptive (barrier, hormonal, implant, or permanent sterilization methods). Women of childbearing potential will be allowed to enroll provided they practice adequate forms of birth control.
• * Physical exam with no evidence of active skin infection and/or other findings that indicate chronic disease or concomitant inflammatory/immune-mediated skin disease other than psoriasis.

Exclusion Criteria:

• For subjects with guttate psoriasis:
• * Subject is unable to provide written informed consent or comply with the protocol.
• * Subject is younger than 18 years of age or older than 70 years.
• * Have a history of active, chronic or recurrent infectious disease including HIV, hepatitis B, or hepatitis C.
• * Have active tuberculosis or latent tuberculosis without at least 4 weeks of treatment with isoniazid.
• * Have current signs or symptoms of severe, progressive, or uncontrolled medical disease.
• * Known allergies, hypersensitivity, or intolerance to guselkumab (TremfyaTM) excipients.
• * Have a known history of lymphoproliferative disease, including lymphoma, or signs and symptoms suggestive of possible lymphoproliferative disease, such as lymphadenopathy and/or splenomegaly.
• * Have any known malignancy or have a history of malignancy (with the exception of basal cell carcinoma, squamous cell carcinoma in situ of the skin, or cervical carcinoma in situ that has been treated with no evidence of recurrence, or squamous cell carcinoma of the skin that has been treated with no evidence of recurrence within 5 years prior to screening)
• * Are pregnant, nursing, or planning a pregnancy while enrolled in the study or for 12 weeks after the study agent injection for women or are planning to father a child while enrolled in the study or for 12 weeks after the last study agent injection.
• * Are participating in another study using an investigational agent or procedure during participation in this study.
• * Have any condition that, in the opinion of the investigator, would compromise the well-being of the subject or the study or prevent the subject from meeting or performing study requirements.
• * Subjects possess other diagnoses that, in the investigator's opinion interfere with the evaluation of the subject's guttate psoriasis.
• * Pre-existing psoriasis of any type for longer than 6 months. (i.e. plaque, guttate, palmoplantar, pustular, erythrodermic)
• * Previous treatment for psoriasis with phototherapy (narrowband ultraviolet (UV) B, broadband UVB, or UVA), systemic agents (methotrexate, acitretin, cyclosporine, apremilast), or biologic agents (etanercept, adalimumab, ustekinumab, secukinumab, etc.)
• For subjects with chronic plaque psoriasis:
• * Subject is unable to provide written informed consent or comply with the protocol.
• * Subject is younger than 18 years of age or older than 70 years.
• * Have a history of active, chronic or recurrent infectious disease, including HIV, hepatitis B, or hepatitis C.
• * Have active tuberculosis or latent tuberculosis without at least 4 weeks of treatment with isoniazid.
• * Have current signs or symptoms of severe, progressive, or uncontrolled medical disease.
• * Known allergies, hypersensitivity, or intolerance to guselkumab (TremfyaTM) excipients.
• * Have a known history of lymphoproliferative disease, including lymphoma, or signs and symptoms suggestive of possible lymphoproliferative disease, such as lymphadenopathy and/or splenomegaly.
• * Have any known malignancy or have a history of malignancy (with the exception of basal cell carcinoma, squamous cell carcinoma in situ of the skin, or cervical carcinoma in situ that has been treated with no evidence of recurrence, or squamous cell carcinoma of the skin that has been treated with no evidence of recurrence within 5 years prior to screening)
• * Are pregnant, nursing, or planning a pregnancy while enrolled in the study or for 12 weeks after the study agent injection for women or are planning to father a child while enrolled in the study or for 12 weeks after the last study agent injection.
• * Are participating in another study using an investigational agent or procedure during participation in this study.
• * Have any condition that, in the opinion of the investigator, would compromise the well-being of the subject or the study or prevent the subject from meeting or performing study requirements.
• * Subjects possess other diagnoses that, in the investigator's opinion, interfere with the evaluation of the subject's plaque psoriasis.
• * Prior history of guttate psoriasis.